List utils

list_utils.erl

-module(list_utils).

-export([group_by/2]).

group_by(_Key, []) -> [];
group_by(Key, List) ->
    [H|T] = lists:keysort(Key, List),
    K = element(Key, H),
    group_by_(Key, K, [H], [], T).

group_by_(_Key, K, Values, Acc, []) ->
    lists:reverse([{K, lists:reverse([Values])}|Acc]);
group_by_(Key, K, Values, Acc, [H|T]) ->
    K2 = element(Key, H),
    case K =:= K2 of
        true ->
            group_by_(Key, K, [H|Values], Acc, T);
        false ->
            group_by_(Key, K2, [H], [{K, lists:reverse(Values)}|Acc], T)
    end.