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-rw-r--r--lib/stdlib/doc/src/maps.xml22
-rw-r--r--lib/stdlib/src/maps.erl21
-rw-r--r--lib/stdlib/test/maps_SUITE.erl14
3 files changed, 50 insertions, 7 deletions
diff --git a/lib/stdlib/doc/src/maps.xml b/lib/stdlib/doc/src/maps.xml
index e46068230a..7345a9357a 100644
--- a/lib/stdlib/doc/src/maps.xml
+++ b/lib/stdlib/doc/src/maps.xml
@@ -33,6 +33,28 @@
<funcs>
<func>
+ <name name="filter" arity="2"/>
+ <fsummary>Choose pairs which satisfy a predicate</fsummary>
+ <desc>
+ <p>
+ Returns a map <c><anno>Map2</anno></c> for which predicate
+ <c><anno>Pred</anno></c> holds true in <c><anno>Map1</anno></c>.
+ </p>
+ <p>
+ The call will fail with a <c>{badmap,Map}</c> exception if
+ <c><anno>Map1</anno></c> is not a map or with <c>badarg</c> if
+ <c><anno>Pred</anno></c> is not a function of arity 2.
+ </p>
+ <p>Example:</p>
+ <code type="none">
+> M = #{a => 2, b => 3, c=> 4, "a" => 1, "b" => 2, "c" => 4},
+ Pred = fun(K,V) -> is_atom(K) andalso (V rem 2) =:= 0 end,
+ maps:filter(Pred,M).
+#{a => 2,c => 4} </code>
+ </desc>
+ </func>
+
+ <func>
<name name="find" arity="2"/>
<fsummary></fsummary>
<desc>
diff --git a/lib/stdlib/src/maps.erl b/lib/stdlib/src/maps.erl
index 3877c150ec..533ff08726 100644
--- a/lib/stdlib/src/maps.erl
+++ b/lib/stdlib/src/maps.erl
@@ -19,7 +19,8 @@
-module(maps).
--export([get/3,fold/3, map/2, size/1,
+-export([get/3,filter/2,fold/3, map/2,
+ size/1,
without/2, with/2]).
@@ -145,6 +146,19 @@ get(Key,Map,Default) ->
erlang:error({badmap,Map},[Key,Map,Default]).
+-spec filter(Pred,Map1) -> Map2 when
+ Pred :: fun((Key, Value) -> boolean()),
+ Key :: term(),
+ Value :: term(),
+ Map1 :: map(),
+ Map2 :: map().
+
+filter(Pred,Map) when is_function(Pred,2), is_map(Map) ->
+ maps:from_list([{K,V}||{K,V}<-maps:to_list(Map),Pred(K,V)]);
+filter(Pred,Map) ->
+ erlang:error(error_type(Map),[Pred,Map]).
+
+
-spec fold(Fun,Init,Map) -> Acc when
Fun :: fun((K, V, AccIn) -> AccOut),
Init :: term(),
@@ -169,10 +183,7 @@ fold(Fun,Init,Map) ->
V2 :: term().
map(Fun,Map) when is_function(Fun, 2), is_map(Map) ->
- maps:from_list(lists:map(fun
- ({K,V}) ->
- {K,Fun(K,V)}
- end,maps:to_list(Map)));
+ maps:from_list([{K,Fun(K,V)}||{K,V}<-maps:to_list(Map)]);
map(Fun,Map) ->
erlang:error(error_type(Map),[Fun,Map]).
diff --git a/lib/stdlib/test/maps_SUITE.erl b/lib/stdlib/test/maps_SUITE.erl
index 1d9c041a74..21e146ae3d 100644
--- a/lib/stdlib/test/maps_SUITE.erl
+++ b/lib/stdlib/test/maps_SUITE.erl
@@ -34,7 +34,7 @@
-export([init_per_testcase/2]).
-export([end_per_testcase/2]).
--export([t_get_3/1,
+-export([t_get_3/1, t_filter_2/1,
t_fold_3/1,t_map_2/1,t_size_1/1,
t_with_2/1,t_without_2/1]).
@@ -45,7 +45,7 @@ suite() ->
[{ct_hooks, [ts_install_cth]}].
all() ->
- [t_get_3,
+ [t_get_3,t_filter_2,
t_fold_3,t_map_2,t_size_1,
t_with_2,t_without_2].
@@ -99,6 +99,16 @@ t_with_2(_Config) ->
?badarg(with,[a,#{}]) = (catch maps:with(a,#{})),
ok.
+t_filter_2(Config) when is_list(Config) ->
+ M = #{a => 2, b => 3, c=> 4, "a" => 1, "b" => 2, "c" => 4},
+ Pred1 = fun(K,V) -> is_atom(K) andalso (V rem 2) =:= 0 end,
+ Pred2 = fun(K,V) -> is_list(K) andalso (V rem 2) =:= 0 end,
+ #{a := 2,c := 4} = maps:filter(Pred1,M),
+ #{"b" := 2,"c" := 4} = maps:filter(Pred2,M),
+ %% error case
+ ?badmap(a,filter,[_,a]) = (catch maps:filter(fun(_,_) -> ok end,id(a))),
+ ?badarg(filter,[<<>>,#{}]) = (catch maps:filter(id(<<>>),#{})),
+ ok.
t_fold_3(Config) when is_list(Config) ->
Vs = lists:seq(1,200),