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:

<cfscript>
/**
 * 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 (&#110;&#97;&#116;&#104;&#97;&#110;&#64;&#99;&#104;&#97;&#110;&#103;&#101;&#109;&#101;&#100;&#105;&#97;&#46;&#99;&#111;&#109;) 
 * @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;
}
</cfscript>