This module contains functions for maps processing.
An iterator representing the associations in a map with keys of type
Created using
Consumed by
Returns a map
The call fails with a
Example:
> 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}
Returns a tuple
The call fails with a
Example:
> Map = #{"hi" => 42},
Key = "hi",
maps:find(Key,Map).
{ok,42}
Calls
The call fails with a
Example:
> Fun = fun(K,V,AccIn) when is_list(K) -> AccIn + V end,
Map = #{"k1" => 1, "k2" => 2, "k3" => 3},
maps:fold(Fun,0,Map).
6
Takes a list of key-value tuples elements and builds a map. The associations can be in any order, and both keys and values in the association can be of any term. If the same key appears more than once, the latter (right-most) value is used and the previous values are ignored.
Example:
> List = [{"a",ignored},{1337,"value two"},{42,value_three},{"a",1}],
maps:from_list(List).
#{42 => value_three,1337 => "value two","a" => 1}
Returns value
The call fails with a
Example:
> Key = 1337,
Map = #{42 => value_two,1337 => "value one","a" => 1},
maps:get(Key,Map).
"value one"
Returns value
The call fails with a
Example:
> Map = #{ key1 => val1, key2 => val2 }.
#{key1 => val1,key2 => val2}
> maps:get(key1, Map, "Default value").
val1
> maps:get(key3, Map, "Default value").
"Default value"
Returns
The call fails with a
Example:
> Map = #{"42" => value}.
#{"42" => value}
> maps:is_key("42",Map).
true
> maps:is_key(value,Map).
false
Returns a map iterator
The call fails with a
Example:
> M = #{ a => 1, b => 2 }.
#{a => 1,b => 2}
> I = maps:iterator(M).
[{a,1},{b,2}]
> {K1, V1, I2} = maps:next(I).
{a,1,[{b,2}]}
> {K2, V2, I3} = maps:next(I2).
{b,2,[]}
> maps:next(I3).
none
Returns a complete list of keys, in any order, which resides
within
The call fails with a
Example:
> Map = #{42 => value_three,1337 => "value two","a" => 1},
maps:keys(Map).
[42,1337,"a"]
Produces a new map
The call fails with a
Example:
> Fun = fun(K,V1) when is_list(K) -> V1*2 end,
Map = #{"k1" => 1, "k2" => 2, "k3" => 3},
maps:map(Fun,Map).
#{"k1" => 2,"k2" => 4,"k3" => 6}
Merges two maps into a single map
The call fails with a
Example:
> Map1 = #{a => "value_one", b => "value_two"},
Map2 = #{a => 1, c => 2},
maps:merge(Map1,Map2).
#{a => 1,b => "value_two",c => 2}
Returns a new empty map.
Example:
> maps:new().
#{}
Returns the next key-value association in
If there are no more associations in the iterator,
Example:
> Map = #{a => 1, b => 2, c => 3}.
#{a => 1,b => 2,c => 3}
> Iter = maps:iterator(Map).
[{a,1},{b,2},{c,3}]
> {_, _, Iter1} = maps:next(Iter).
{a,1,[{b,2},{c,3}]}
> {_, _, Iter2} = maps:next(Iter1).
{b,2,[{c,3}]}
> {_, _, Iter3} = maps:next(Iter2).
{c,3,[]}
> maps:next(Iter3).
none
Associates
The call fails with a
Example:
> Map = #{"a" => 1}.
#{"a" => 1}
> maps:put("a", 42, Map).
#{"a" => 42}
> maps:put("b", 1337, Map).
#{"a" => 1,"b" => 1337}
Removes the
The call fails with a
Example:
> Map = #{"a" => 1}.
#{"a" => 1}
> maps:remove("a",Map).
#{}
> maps:remove("b",Map).
#{"a" => 1}
Returns the number of key-value associations in
Example:
> Map = #{42 => value_two,1337 => "value one","a" => 1},
maps:size(Map).
3
The function removes the
The call will fail with a
Example:
> Map = #{"a" => "hello", "b" => "world"}.
#{"a" => "hello", "b" => "world"}
> maps:take("a",Map).
{"hello",#{"b" => "world"}}
> maps:take("does not exist",Map).
error
Returns a list of pairs representing the key-value associations of
The call fails with a
Example:
> Map = #{42 => value_three,1337 => "value two","a" => 1},
maps:to_list(Map).
[{42,value_three},{1337,"value two"},{"a",1}]
If
The call fails with a
Example:
> Map = #{"a" => 1}.
#{"a" => 1}
> maps:update("a", 42, Map).
#{"a" => 42}
Update a value in a
Example:
> Map = #{"counter" => 1},
Fun = fun(V) -> V + 1 end,
maps:update_with("counter",Fun,Map).
#{"counter" => 2}
Update a value in a
Example:
> Map = #{"counter" => 1},
Fun = fun(V) -> V + 1 end,
maps:update_with("new counter",Fun,42,Map).
#{"counter" => 1,"new counter" => 42}
Returns a complete list of values, in arbitrary order, contained in
map
The call fails with a
Example:
> Map = #{42 => value_three,1337 => "value two","a" => 1},
maps:values(Map).
[value_three,"value two",1]
Returns a new map
Example:
> Map = #{42 => value_three,1337 => "value two","a" => 1},
Ks = ["a",42,"other key"],
maps:with(Ks,Map).
#{42 => value_three,"a" => 1}
Returns a new map
Example:
> Map = #{42 => value_three,1337 => "value two","a" => 1},
Ks = ["a",42,"other key"],
maps:without(Ks,Map).
#{1337 => "value two"}