Question

I have a number array and I’d like to calculate the median.
When the array is odd, the calculation is OK, when it’s even strange number comes up.

private var numbers:String = "2,5,3,4,6,1";
private var array:Array = numbers.split(",");

private function getMedian(array:Array):Number {
 var sortnums:Array = array.sort(Array.NUMERIC);
 var length:Number = sortnums.length;
 var mid1:Number; var mid2:Number; var median:Number;

 if(length % 2 == 0){
     mid1 = length / 2; trace("mid1: "+mid1);
 mid2= ((length - 1) / 2)-0.5; trace("mid2: "+mid2);
 trace ("mid1: "+sortnums[mid1]+", mid2: "+sortnums[mid2]);
 median = (sortnums[mid1] + sortnums[mid2]) / 2;
 }else{
 mid1 = (length / 2)-0.5
 median = sortnums[mid1]
 }
 trace (median);
 return median;
}

The result is 21.5, but should be 3.5

mid1 and mid2 are a position in the array.

Could somebody help?

Answer 1

Try this (for tidyness):

function getMedian(plug:Array):Number
{
    // Even length.
    if(plug.length % 2 == 0)
    {
        var a:Number = plug[int(plug.length / 2) - 1];
        var b:Number = plug[int(plug.length / 2)];

        return (a + b) / 2;
    }

    // Odd length.
    return plug[int(plug.length / 2)];
}


// Tests.
trace(getMedian([2,5,3,4,6,1])); // 3.5
trace(getMedian([2,5,3,4,6])); // 3

By the way, I’m fairly certain your code is working fine, the problem is that you’re doing this as a string concatenation rather than a number sum here:

median = (sortnums[mid1] + sortnums[mid2]) / 2;

Meaning you’re literally adding the string 1.5 onto 2 and getting 21.5 rather than 3.5.

Try amending your code so it reads like so:

median = (Number(sortnums[mid1]) + Number(sortnums[mid2])) / 2;