Erlang Standard library Maps

new ()-#{}

Returns a new, empty mapping group.

1> maps:new ().

#{}

to_list (M), [{K1,v1}, ..., {KN,VN}]

Converts all keys and values in the mapping group M to a list of key values. The keys are sorted in ascending order in the generated list.

1> M = #{age = +, name + DMM}.

#{age = 18,name = DMM}

2> maps:to_list (M).

[{AGE,18},{NAME,DMM}]

From_list ([{k1,v1},..., {KN,VN}]), M

Converts a list of key-value pairs into a mapping group M. If the same key appears more than once, the last value associated with the list is used, and the preceding values are ignored.

1> T = [{age,18},{name,dmm},{age,19}].

[{age,18},{name,dmm},{age,19}]

2> maps:from_list (T).

#{age = 19,name = DMM}

size (Map), Integer () >= 0

Returns the number of entries in the Mapping group.

1> Map = #{42 = value_two,1337 = "Value One", "a" and "= 1}".

#{42 = value_two,1337 = "Value One", "a" and "= 1}"

2> maps:size (MAP).

3

Is_key (Key, MAP), BOOL ()

Returns true if the mapping group contains an entry with key keys, otherwise false is returned.

1> Map = #{"All" and "= value".

#{"+" = value}

2> Maps:is_key ("a", Map).

True

3> Maps:is_key (Value,map).

False

get (Key, Map), Val

Returns the value associated with the Key in the mapping group, or throws an exception error.

1> Map = #{42 = value_two,1337 = "Value One", "a" and "= 1}".

#{42 = value_two,1337 = "Value One", "a" and "= 1}"

2> Maps:get ("a", Map).

1

3> Maps:get (2,map).

* * Exception error: {badkey,2}

in function MAPS:GET/2

Called as maps:get (2,#{42 = value_two,1337 = "Value One", "a" and "= 1}")

get (Key, Map, Default), Value | Default

Returns the value associated with the key in the mapping group, and throws a default value if no key is available.

1> Map = #{Key1 = val1, Key2 = Val2}.

#{key1 = Val1,key2 = Val2}

2> Maps:get (Key1, Map, "Default value").

Val1

3> Maps:get (Key3, Map, "Default value").

"Default value"

Find (Key, Map), {OK, Value} | Error

Returns the value associated with the Key in the mapping group, otherwise returns an error.

1> Map = #{"Hi" = 42}.

#{"HI" = 42}

2> maps:find ("Hi", Map).

{ok,42}

3> maps:find ("HI", Map).

Error

keys (MAP), [Key1,.. KeyN]

Returns a list of the keys contained in the mapping group, sorted in ascending order.

1> Map = #{42 = value_three,1337 = "Value", "a" and "= 1}".

#{42 = value_three,1337 = "Value", "a" and "= 1}"

2> Maps:keys (MAP).

[42,1337, "a"]

Remove (Key, M), M1

Returns a new mapping group M1 except for keys that are key, except that the others are identical to M.

1> Map = #{"a" = 1}.

#{"A" = 1}

2> Maps:remove ("a", Map).

#{}

3> Maps:remove ("B", Map).

#{"A" = 1}

with ([Key1,.., KeyN], Map1), Map2

Returns a new mapping group MAP2, which is an assignment of MAP1, but has only the elements of these keys in the [Key1, ..., KeyN] list.

1> Map = #{42 = value_three,1337 = "Value", "a" and "= 1}".

#{42 = value_three,1337 = "Value", "a" and "= 1}"

2> Maps:with (["A", "a", "a", "other"],map).

#{42 = Value_three, "a" = 1}

without ([Key1,..., keyn],m), M1

Returns a new mapping group M1, which is a copy of M, except for the elements of these keys in the list with [Key1, ..., KeyN].

1> Map = #{42 = value_three,1337 = "Value", "a" and "= 1}".

#{42 = value_three,1337 = "Value", "a" and "= 1}"

2> Maps:without (["A", "a", "a", "other"],map).

#{1337 = "Value"}

Erlang Standard library Maps