Erlang (programming language)/Tutorials/Lists

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Lists Module

Lists provides list functions. There is a non-standard parallel version available called plists.

Filter

1> F1 = fun(Item) -> length(Item) > 1 end. 
#Fun<erl_eval.6.58606484>
2> lists:filter(F1, [[1],[1,2],[1,2,3]]).
[[1,2,3],[1,2]]

Flatten

lists:flatten([[1,2],[3,4]]).
[1,2,3,4]

Fold(left)

3> lists:foldl( fun(X, Prod)-> X*Prod end, 1, [1,2,3,4,5]).
120 

Fold(right)

3> lists:foldr( fun(X, Prod)-> X*Prod end, 1, [1,2,3,4,5]).
120 

Map

6> Sqrt = fun(X) -> math:sqrt(X) end.
#Fun<erl_eval.6.56006484>

7> lists:map(Sqrt,[1,2,3,4]).
[1.00000,1.41421,1.73205,2.00000]

Mapfold(left)

lists:mapfoldl(fun(X,Prod)->{X,X*Prod} end, 1, [1,2,3,4,5]).
{[1,2,3,4,5], 120}

Mapfold(right)

lists:mapfoldr(fun(X,Prod)->{X,X*Prod} end, 1, [1,2,3,4,5]).
{[1,2,3,4,5], 120}

Nth

lists:nth(1,[a,b,c]).
a

Nthtail

lists:nthtail(2,[a,b,c,d]).
[c,d]

Sort

Note: sort will work with any combination of types. Each type has a natural sort order.

lists:sort([2,4,3,5]).
[2,3,4,5]

lists:sort([1, 2, b, a, self(), fun()->true]).
[1, 2, a, b, #Fun<erl.20.117942222>, <0,176,0>]