Finding Elements in One Array but Not Another
From Erlang Community
You want to find elements that are in one list but not another.
You want to find elements in list A that aren't in list B. Erlang provides several ways of doing this:
Use the lists:subtract Function
The lists module provides the subtract function, which takes two list and returns a new copy of the first list, such that the first occurrence of each element of the second list is removed. For example:
1> A = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] 2> B = [2,4,6,8,9,10,12,14,15,16]. [2,4,6,8,9,10,12,14,15,16]. 3> lists:subtract(A,B). [1,3,5,7,11,13]
Note: Erlang provides native list operators for concatentation (++) and subtraction (--). The subtraction operator provides the same functionality as the lists:subtract function:
4> A -- B. [1,3,5,7,11,13]
Iterate over the two lists
You can iterate over the two lists (using the lists:foreach function), and filter out any entries from list A that are also members of list B.
5> lists:foldl(fun(X,ACC) -> Y=lists:member(X, B), 5> if Y -> [X|ACC]; 5> true -> ACC 5> end end, , lists:reverse(A)). [2,4,6,8,9,10,12,14,15,16]