Shim for basic statistical analysis methods on Array. Includes max, min, median, sum, mean, variance, and standard deviation.

stats.coffee

# max
if "function" isnt typeof Array::max
  Array::max = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.max called on null or undefined")  if null is this or "undefined" is typeof this

    Math.max.apply null, this

# min
if "function" isnt typeof Array::min
  Array::min = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.min called on null or undefined")  if null is this or "undefined" is typeof this

    Math.min.apply null, this

# median
if "function" isnt typeof Array::median
  Array::median = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.median called on null or undefined")  if null is this or "undefined" is typeof this

    # locals
    sorted = @sort (a,b) => return a - b
    length = @length >>> 0
    half   = Math.floor length/2

    if length % 2
      return this[half]
    else
      return [this[half - 1], this[half]].mean()

# sum
# depends on Array.prototype.reduce to work properly.
# shim for that available here https://gist.github.com/l3ck/6418510
if "function" isnt typeof Array::sum
  Array::sum = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.sum called on null or undefined")  if null is this or "undefined" is typeof this

    @reduce (a, b) ->
      a + b

# mean
if "function" isnt typeof Array::mean
  Array::mean = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.mean called on null or undefined")  if null is this or "undefined" is typeof this

    length = @length >>> 0

    @sum()/length

# variance
if "function" isnt typeof Array::variance
  Array::variance = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.variance called on null or undefined")  if null is this or "undefined" is typeof this

    index  = 0
    length = @length >>> 0
    mean   = @mean()
    powed  = []

    # loop to generate powed
    while length > index
      continue unless @hasOwnProperty(index)
      powed.push Math.pow(this[index] - mean, 2)
      ++index

    # return mean of powed
    powed.mean()

# standard deviation
if "function" isnt typeof Array::stddev
  Array::stddev = ->
    "use strict"

    # throw on null
    throw new TypeError("Array.prototype.stddev called on null or undefined")  if null is this or "undefined" is typeof this

    # square root of variance
    Math.sqrt @variance()