Source for file StatisticsHandler.class.php

<?php
 
//require_once(HARMONI.'utilities/StatisticsHandler.interface.php');
/**
 * An interface to calculate various statistical information.
 *
 * @package harmoni.utilities
 * 
 * @copyright Copyright &copy; 2005, Middlebury College
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License (GPL)
 *
 * @version $Id: StatisticsHandler.class.php,v 1.4 2007/09/04 20:25:54 adamfranco Exp $
 */
class StatisticsHandler {
 
    var $_data;
    var $_sortedData;
 
    var $_mean, $_median, $_discrimination, $_standardDeviation, $_max, $_min;
 
   /**
    * Create a Add a handler with given information.
    * @param object $data The object, which contains all the data. It should be provided with methods: next(), getNext() and getSize().
    * @return boolean Wheter all data is numeric.
    * @access public
    */    
 
    function StatisticsHandler($data) { 
        if(is_array($data)){
            $this->_data = $data;
        }
        else{
            $this->_data = array();
            
            while($data->hasNext())
                $this->_data[] = $data->next();
        }
        return $this->_checkdata();
    }
 
   /**
    * Return the mean value of the data.
    * @return float The mean value of the data.
    * @access public
    */
    function getMean() { 
        if(!isset($this->_mean)){
            $sum = 0;
            foreach($this->_data as $value)
                $sum += $value;
 
            $sum = round($sum/count($this->_data),3);
            
            $this->_mean = $sum;
        }
 
        return $this->_mean;
    }
 
   /**
    * Return the median value of the data.
    * @return float The median value of the data.
    * @access public
    */
    function getMedian() { 
        if(!isset($this->_median)){
            if(!isset($this->_sortedData)){
                $this->_sortedData = $this->_data;
                sort($this->_sortedData);
            }
            
            $this->_median = $this->_sortedData[count($this->_sortedData)/2];
        }
 
        return $this->_median;
    }
 
 
   /**
    * Return the standard deviation of the data.
    * @return float The standard deviation of  the data.
    * @access public
    */
    function getStandardDeviation() { 
        if(!isset($this->_standardDeviation)) {
            $mean = $this->getMean();
            
            $variance = 0;
    
            foreach($this->_data as $value)
                $variance += ($mean-$value)*($mean-$value);
 
            $this->_standardDeviation = round(sqrt($variance/count($this->_data)),3);
        }
 
        return $this->_standardDeviation;
    }
 
   /**
    * Return the modal (most frequent value) of the data.
    * @return float The modal (most frequent value) of the data.
    * @access public
    */
    function getModal() { 
        if (!isset($this->_modal)) {
            $cf=0; $mf=0; $current = '';
            foreach ($this->_data as $value) {
                if ($value == $current)
                    $cf++;
                else {
                    if ($cf>$mf){
                        $mf = $cf;
                        $mv = $current;
                    }
                    $current = $value;
                    $cf = 1;
                }
            }
            if ($cf>$mf)
                $mv = $cv;
            
            $this->_modal = $mv;
        }
        
        return $this->_modal;
    }
 
   /**
    * Return the maximum value of the data.
    * @return float The maximum value of the data.
    * @access public
    */
    function getMax() { 
        if(!isset($this->_max)){
            if(!isset($this->_sortedData)){
                $this->_sortedData = $this->_data;
                sort($this->_sortedData);
            }
            $this->_max = $this->_sortedData[count($this->_sortedData)-1];
            $this->_min = $this->_sortedData[0];
        }
 
        return $this->_max;
    }
 
   /**
    * Return the minimum value of the data.
    * @return float The minimum value of the data.
    * @access public
    */
    function getMin() { 
        if(!isset($this->_min)){
            if(!isset($this->_sortedData)){
                $this->_sortedData = $this->_data;
                sort($this->_sortedData);
            }
            $this->_max = $this->_sortedData[count($this->_sortedData)-1];
            $this->_min = $this->_sortedData[0];
        }
 
        return $this->_min;
    }
 
   /**
    * Return the discrimination value of the data. Discrimination is the difference between
    * the mean value of the top 27% and the mean value of the bottom 27% calculated separately. In the case of test results
    * the discrimination ranges from 0 to 100, so divide the result by 100 before printing.
    * @return float The discrimination value of the data.
    * @access public
    */
    function getDiscrimination() { 
        if(!isset($this->_discrimination)){
            if(!isset($this->_sortedData)){
                $this->_sortedData = $this->_data;
                sort($this->_sortedData);
            }
 
            $sum1 = 0;
            $sum2 = 0;
 
            $dataSize = count($this->_data);
            $size = round($dataSize*27.0/100);
 
            for($ii=0;$ii<$size;$ii++){
                $sum1 += $this->_sortedData[$ii];
                $sum2 += $this->_sortedData[$dataSize-$ii-1];
            }
            
            $sum1 /= $size;    
            $sum2 /= $size;    
 
            $this->_discrimination = round($sum2 - $sum1,3);
        }
 
        return $this->_discrimination;
    }
 
   /**
    * Return the Discrimination of a different set in accordance to the base set.
    * The function will take the results of the original, calculate who got the top 27% of them and see how these compare
    * to the results of the second data. The same will be done for the bottom 27%, after which the results will be substracted.
    * This should be used if the original data is the overall results of the test and the second set is the results of one particular question.
    * @param object $secondData The data to get the discrimination from. It should have the same number of elements as the original data and
    *  The values should be in the same order as the original.
    *  Clearly $secondData should either be an array or also have next() and  hasNext().
    * @return float The discrimination of the second set in accordance with the first.
    * @access public
    */
    function getSecondaryDiscrimination($secondData) { 
        if (is_array($secondData))
            $second = $secondData;
        else {
            $second = array();
            while($secondData->hasNext())
                $second[] = $secondData->next();
        }
 
        $first = $this->_data;
 
        array_multisort($first,$second);
 
        $sum1 = 0;
        $sum2 = 0;
 
        $dataSize = count($second);
        $size = round($dataSize*27.0/100);
 
        for($ii=0;$ii<$size;$ii++){
            $sum1 += $second[$ii];
            $sum2 += $second[$dataSize-$ii-1];
        }
 
        $sum1 /= $size;
        $sum2 /= $size;    
 
        return round($sum2 - $sum1,3);
    }
 
   /**
    * Check if all the data is numerically interpretable (only contains numbers and numeric strings)
    * @return boolean Whether all data is float interpretable.
    * @access private
    */
    function _checkdata() {
        foreach ($this->_data as $value)
            if(!is_numeric($value))    
                return false;
        return true;
    }
}
 
 
 
?>