diff options
Diffstat (limited to 'lib/stdlib')
| -rw-r--r-- | lib/stdlib/doc/src/lists.xml | 25 | ||||
| -rw-r--r-- | lib/stdlib/src/lists.erl | 24 | ||||
| -rw-r--r-- | lib/stdlib/test/lists_SUITE.erl | 4 |
3 files changed, 44 insertions, 9 deletions
diff --git a/lib/stdlib/doc/src/lists.xml b/lib/stdlib/doc/src/lists.xml index b6c0fa4e05..1aff78f4fc 100644 --- a/lib/stdlib/doc/src/lists.xml +++ b/lib/stdlib/doc/src/lists.xml @@ -152,6 +152,31 @@ </desc> </func> <func> + <name name="filtermap" arity="2"/> + <fsummary>Filter and map elements which satisfy a function</fsummary> + <desc> + <p>Calls <c><anno>Fun</anno>(<anno>Elem</anno>)</c> on successive elements <c>Elem</c> + of <c><anno>List1</anno></c>. <c><anno>Fun</anno>/2</c> must return either a boolean + or a tuple <c>{true, <anno>Value</anno>}</c>. The function returns the list of elements + for which <c><anno>Fun</anno></c> returns a new value, where a value of <c>true</c> + is synonymous with <c>{true, <anno>Elem</anno>}</c>.</p> + <p>That is, <c>filtermap</c> behaves as if it had been defined as follows:</p> + <code type="none"> +filtermap(Fun, List1) -> + lists:foldr(fun(Elem, Acc) -> + case Fun(Elem) of + false -> Acc; + true -> [Elem|Acc]; + {true,Value} -> [Value|Acc] + end, + end, [], List1).</code> + <p>Example:</p> + <pre> +> <input>lists:filtermap(fun(X) -> case X rem 2 of 0 -> {true, X div 2}; _ -> false end end, [1,2,3,4,5]).</input> +[1,2]</pre> + </desc> + </func> + <func> <name name="flatlength" arity="1"/> <fsummary>Length of flattened deep list</fsummary> <desc> diff --git a/lib/stdlib/src/lists.erl b/lib/stdlib/src/lists.erl index 961c060019..0c033acd88 100644 --- a/lib/stdlib/src/lists.erl +++ b/lib/stdlib/src/lists.erl @@ -36,7 +36,7 @@ -export([merge/3, rmerge/3, sort/2, umerge/3, rumerge/3, usort/2]). -export([all/2,any/2,map/2,flatmap/2,foldl/3,foldr/3,filter/2, - partition/2,zf/2, + partition/2,zf/2,filtermap/2, mapfoldl/3,mapfoldr/3,foreach/2,takewhile/2,dropwhile/2,splitwith/2, split/2]). @@ -1291,18 +1291,28 @@ partition(Pred, [H | T], As, Bs) -> partition(Pred, [], As, Bs) when is_function(Pred, 1) -> {reverse(As), reverse(Bs)}. --spec zf(fun((T) -> boolean() | {'true', X}), [T]) -> [(T | X)]. +-spec filtermap(Fun, List1) -> List2 when + Fun :: fun((Elem) -> boolean() | {'true', Value}), + List1 :: [Elem], + List2 :: [Elem | Value], + Elem :: term(), + Value :: term(). -zf(F, [Hd|Tail]) -> +filtermap(F, [Hd|Tail]) -> case F(Hd) of true -> - [Hd|zf(F, Tail)]; + [Hd|filtermap(F, Tail)]; {true,Val} -> - [Val|zf(F, Tail)]; + [Val|filtermap(F, Tail)]; false -> - zf(F, Tail) + filtermap(F, Tail) end; -zf(F, []) when is_function(F, 1) -> []. +filtermap(F, []) when is_function(F, 1) -> []. + +-spec zf(fun((T) -> boolean() | {'true', X}), [T]) -> [(T | X)]. + +zf(F, L) -> + filtermap(F, L). -spec foreach(Fun, List) -> ok when Fun :: fun((Elem :: T) -> term()), diff --git a/lib/stdlib/test/lists_SUITE.erl b/lib/stdlib/test/lists_SUITE.erl index b56f0b39d8..cd7210f8ec 100644 --- a/lib/stdlib/test/lists_SUITE.erl +++ b/lib/stdlib/test/lists_SUITE.erl @@ -2532,8 +2532,8 @@ otp_5939(Config) when is_list(Config) -> ?line [] = lists:filter(Pred, []), ?line {'EXIT', _} = (catch lists:partition(func, [])), ?line {[],[]} = lists:partition(Pred, []), - ?line {'EXIT', _} = (catch lists:zf(func, [])), - ?line [] = lists:zf(Fun1, []), + ?line {'EXIT', _} = (catch lists:filtermap(func, [])), + ?line [] = lists:filtermap(Fun1, []), ?line {'EXIT', _} = (catch lists:foreach(func, [])), ?line ok = lists:foreach(Fun1, []), ?line {'EXIT', _} = (catch lists:mapfoldl(func, [], [])), |