median is the 'middle number' of a list. often medians are useful when the list contains extreme values and the average would be skewed by outliers

median = (x) ->

The median of an empty list is null

    return null if (x.length == 0)

Sorting the array makes it easy to find the center, but use .slice() to ensure the original array x is not modified

    sorted = x.slice().sort((a, b) -> a - b)

If the length of the list is odd, the median is the central number

    if (sorted.length % 2 == 1)
        sorted[(sorted.length - 1) / 2]
    else

Otherwise, the median is the average of the two numbers at the center of the list

        (sorted[(sorted.length / 2) - 1] +
        sorted[(sorted.length / 2)]) / 2