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<?php
/**
 * PHPExcel
 *
 * Copyright (c) 2006 - 2013 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * @category    PHPExcel
 * @package             PHPExcel_Calculation
 * @copyright   Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license             http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt   LGPL
 * @version             ##VERSION##, ##DATE##
 */


/** PHPExcel root directory */
if (!defined('PHPEXCEL_ROOT')) {
        /**
         * @ignore
         */
        define('PHPEXCEL_ROOT', dirname(__FILE__) . '/../../');
        require(PHPEXCEL_ROOT . 'PHPExcel/Autoloader.php');
}


/**
 * PHPExcel_Calculation_Database
 *
 * @category    PHPExcel
 * @package             PHPExcel_Calculation
 * @copyright   Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 */
class PHPExcel_Calculation_Database {


        /**
         * __fieldExtract
         *
         * Extracts the column ID to use for the data field.
         *
         * @access      private
         * @param       mixed[]         $database               The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       mixed           $field                  Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @return      string|NULL
         *
         */
        private static function __fieldExtract($database,$field) {
                $field = strtoupper(PHPExcel_Calculation_Functions::flattenSingleValue($field));
                $fieldNames = array_map('strtoupper',array_shift($database));

                if (is_numeric($field)) {
                        $keys = array_keys($fieldNames);
                        return $keys[$field-1];
                }
                $key = array_search($field,$fieldNames);
                return ($key) ? $key : NULL;
        }

        /**
         * __filter
         *
         * Parses the selection criteria, extracts the database rows that match those criteria, and
         * returns that subset of rows.
         *
         * @access      private
         * @param       mixed[]         $database               The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       mixed[]         $criteria               The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      array of mixed
         *
         */
        private static function __filter($database,$criteria) {
                $fieldNames = array_shift($database);
                $criteriaNames = array_shift($criteria);

                //      Convert the criteria into a set of AND/OR conditions with [:placeholders]
                $testConditions = $testValues = array();
                $testConditionsCount = 0;
                foreach($criteriaNames as $key => $criteriaName) {
                        $testCondition = array();
                        $testConditionCount = 0;
                        foreach($criteria as $row => $criterion) {
                                if ($criterion[$key] > '') {
                                        $testCondition[] = '[:'.$criteriaName.']'.PHPExcel_Calculation_Functions::_ifCondition($criterion[$key]);
                                        $testConditionCount++;
                                }
                        }
                        if ($testConditionCount > 1) {
                                $testConditions[] = 'OR('.implode(',',$testCondition).')';
                                $testConditionsCount++;
                        } elseif($testConditionCount == 1) {
                                $testConditions[] = $testCondition[0];
                                $testConditionsCount++;
                        }
                }

                if ($testConditionsCount > 1) {
                        $testConditionSet = 'AND('.implode(',',$testConditions).')';
                } elseif($testConditionsCount == 1) {
                        $testConditionSet = $testConditions[0];
                }

                //      Loop through each row of the database
                foreach($database as $dataRow => $dataValues) {
                        //      Substitute actual values from the database row for our [:placeholders]
                        $testConditionList = $testConditionSet;
                        foreach($criteriaNames as $key => $criteriaName) {
                                $k = array_search($criteriaName,$fieldNames);
                                if (isset($dataValues[$k])) {
                                        $dataValue = $dataValues[$k];
                                        $dataValue = (is_string($dataValue)) ? PHPExcel_Calculation::_wrapResult(strtoupper($dataValue)) : $dataValue;
                                        $testConditionList = str_replace('[:'.$criteriaName.']',$dataValue,$testConditionList);
                                }
                        }
                        //      evaluate the criteria against the row data
                        $result = PHPExcel_Calculation::getInstance()->_calculateFormulaValue('='.$testConditionList);
                        //      If the row failed to meet the criteria, remove it from the database
                        if (!$result) {
                                unset($database[$dataRow]);
                        }
                }

                return $database;
        }


        /**
         * DAVERAGE
         *
         * Averages the values in a column of a list or database that match conditions you specify.
         *
         * Excel Function:
         *              DAVERAGE(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DAVERAGE($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }
                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::AVERAGE($colData);
        }       //      function DAVERAGE()


        /**
         * DCOUNT
         *
         * Counts the cells that contain numbers in a column of a list or database that match conditions
         * that you specify.
         *
         * Excel Function:
         *              DCOUNT(database,[field],criteria)
         *
         * Excel Function:
         *              DAVERAGE(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      integer
         *
         * @TODO        The field argument is optional. If field is omitted, DCOUNT counts all records in the
         *                      database that match the criteria.
         *
         */
        public static function DCOUNT($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::COUNT($colData);
        }       //      function DCOUNT()


        /**
         * DCOUNTA
         *
         * Counts the nonblank cells in a column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DCOUNTA(database,[field],criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      integer
         *
         * @TODO        The field argument is optional. If field is omitted, DCOUNTA counts all records in the
         *                      database that match the criteria.
         *
         */
        public static function DCOUNTA($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::COUNTA($colData);
        }       //      function DCOUNTA()


        /**
         * DGET
         *
         * Extracts a single value from a column of a list or database that matches conditions that you
         * specify.
         *
         * Excel Function:
         *              DGET(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      mixed
         *
         */
        public static function DGET($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                if (count($colData) > 1) {
                        return PHPExcel_Calculation_Functions::NaN();
                }

                return $colData[0];
        }       //      function DGET()


        /**
         * DMAX
         *
         * Returns the largest number in a column of a list or database that matches conditions you that
         * specify.
         *
         * Excel Function:
         *              DMAX(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DMAX($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::MAX($colData);
        }       //      function DMAX()


        /**
         * DMIN
         *
         * Returns the smallest number in a column of a list or database that matches conditions you that
         * specify.
         *
         * Excel Function:
         *              DMIN(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DMIN($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::MIN($colData);
        }       //      function DMIN()


        /**
         * DPRODUCT
         *
         * Multiplies the values in a column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DPRODUCT(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DPRODUCT($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_MathTrig::PRODUCT($colData);
        }       //      function DPRODUCT()


        /**
         * DSTDEV
         *
         * Estimates the standard deviation of a population based on a sample by using the numbers in a
         * column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DSTDEV(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DSTDEV($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::STDEV($colData);
        }       //      function DSTDEV()


        /**
         * DSTDEVP
         *
         * Calculates the standard deviation of a population based on the entire population by using the
         * numbers in a column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DSTDEVP(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DSTDEVP($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::STDEVP($colData);
        }       //      function DSTDEVP()


        /**
         * DSUM
         *
         * Adds the numbers in a column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DSUM(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DSUM($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_MathTrig::SUM($colData);
        }       //      function DSUM()


        /**
         * DVAR
         *
         * Estimates the variance of a population based on a sample by using the numbers in a column
         * of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DVAR(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DVAR($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::VARFunc($colData);
        }       //      function DVAR()


        /**
         * DVARP
         *
         * Calculates the variance of a population based on the entire population by using the numbers
         * in a column of a list or database that match conditions that you specify.
         *
         * Excel Function:
         *              DVARP(database,field,criteria)
         *
         * @access      public
         * @category Database Functions
         * @param       mixed[]                 $database       The range of cells that makes up the list or database.
         *                                                                              A database is a list of related data in which rows of related
         *                                                                              information are records, and columns of data are fields. The
         *                                                                              first row of the list contains labels for each column.
         * @param       string|integer  $field          Indicates which column is used in the function. Enter the
         *                                                                              column label enclosed between double quotation marks, such as
         *                                                                              "Age" or "Yield," or a number (without quotation marks) that
         *                                                                              represents the position of the column within the list: 1 for
         *                                                                              the first column, 2 for the second column, and so on.
         * @param       mixed[]                 $criteria       The range of cells that contains the conditions you specify.
         *                                                                              You can use any range for the criteria argument, as long as it
         *                                                                              includes at least one column label and at least one cell below
         *                                                                              the column label in which you specify a condition for the
         *                                                                              column.
         * @return      float
         *
         */
        public static function DVARP($database,$field,$criteria) {
                $field = self::__fieldExtract($database,$field);
                if (is_null($field)) {
                        return NULL;
                }

                //      reduce the database to a set of rows that match all the criteria
                $database = self::__filter($database,$criteria);
                //      extract an array of values for the requested column
                $colData = array();
                foreach($database as $row) {
                        $colData[] = $row[$field];
                }

                // Return
                return PHPExcel_Calculation_Statistical::VARP($colData);
        }       //      function DVARP()


}       //      class PHPExcel_Calculation_Database