[digg-reddit-me]I’ll be putting up some statistical functions I’ve had to write recently.  This is the first batch.  I confess, I find the erlang implementations far more readable than the pure math definitions one finds around; I’ve been thinking about writing tutorials, but with this code here, I’m not entirely sure it’s necessary.

At any rate, the code follows.  As with so much of my erlang code, this code is part of the ScUtil library.  ScUtil is free and MIT license, because the GPL is evil.

There’re more statistics coming, I just don’t want to make any one post too huge, and I don’t want keyword saturation.

This partially closes issue 119.  This closes issue 133.  This closes issue 136.  This closes issue 137.

list_product(List) when is_list(List) ->
    list_product(List, 1).

list_product([], Counter) ->
    Counter;

list_product([Head|Tail], Counter) ->
    list_product(Tail, Counter*Head).

arithmetic_mean(List) when is_list(List) ->
    lists:sum(List) / length(List).

geometric_mean(List) when is_list(List) ->
    math:pow(scutil:list_product(List), 1/length(List)).

harmonic_mean(List) when is_list(List) ->
    length(List) / lists:sum([ 1/X || X<-List ]).

weighted_arithmetic_mean(List) when is_list(List) ->
    weighted_arithmetic_mean(List, 0, 0).

weighted_arithmetic_mean([], Num, Denom) ->
    Num/Denom;

weighted_arithmetic_mean([{W,V}|Tail], Num, Denom) ->
    weighted_arithmetic_mean(Tail, Num+(W*V), Denom+W).