CFLib.org – Common Function Library Project

Description:
This function is used to get the percentile rank of a given number from a population of numbers. The percentile refers to the percent of numbers in the set that are below the number you pass in.

Return Values:
Returns a numeric percent value

Example:

<cfset population="33,29,29,31,32,33,33,35,37,25,28">
<cfset array = listToArray(population)>
<table>
    <tr>
        <td>Number to Check</td>
        <td>Percentile</td>
    </tr>
<cfoutput>
<cfloop from="1" to="#arraylen(array)#" index="ii">
    <cfset thisNumber = array[ii]>
    <tr>
        <td>#thisNumber#</td>
        <td>#percentile(thisNumber,array)#</td>
    </tr>
</cfloop>
</cfoutput>
</table>

Parameters:

Full UDF Source:

/**
 * Function for calculating the percentile of a given number from a population of numbers.
 * 
 * @param number      The number you want to get the percentile rank of 
 * @param aPopulation      An array of numbers which is the population to find the percentile in 
 * @param insertNumber      Boolean value to decide if the number should be inserted into the population before calculation.  By default this is false. 
 * @return Returns a numeric percent value 
 * @author Nathan Dintenfass (nathan@changemedia.com) 
 * @version 1, July 30, 2001 
 */
function percentile(numberToCheck,populationArray){
    // (Thanks to Jim Flannery for pointing me at the formula).
    var ii = 1;
    //set a counter for the number below this value
    var countBelow = 0;
    //set a counter for how many instances of thisNumber there are
    var countWithin = 0;
    // deal with the optional parameter as to whether the number to check is to be added to the population.
    //if there a third argument and it is a boolean and it is true, insert the number to check 
    if(arraylen(arguments) gt 2 AND isBoolean(arguments[3]) and arguments[3])
        arrayAppend(populationArray,numberToCheck);
    //now, let's sort the array to make it easier to find the values
    arraySort(populationArray,"numeric");
    //loop through the array, setting the counters appropriately
    for(ii = 1; ii lte arraylen(populationArray); ii = ii + 1){
        //if this number is below numberToCheck, increment the countBelow
        if(populationArray[ii] lt numberToCheck){
            countBelow = countBelow + 1;
        }
        else{
            //if this number is equal to numberToCheck, increment the counterWithin
            if(populationArray[ii] eq numberToCheck){
                countWithin = countWithin + 1;
            }
            //if this number is above the numberToCheck break
            else{
                break;
            }
        }
    }
    //run the percentile formula and return
    return ((countBelow + 0.5 * countWithin)/arraylen(populationArray))*100;
}