# orddict

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Module

orddict

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Module Summary

Key-value dictionary as ordered list.

###
Description

This module provides a Key-Value dictionary. An orddict is a representation of a dictionary, where a list of pairs is used to store the keys and values. The list is ordered after the keys in the Erlang term order.

This module provides the same interface as the dict(3) module but with a defined representation. One difference is that while dict considers two keys as different if they do not match (=:=), this module considers two keys as different if and only if they do not compare equal (==).

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Data Types

####
orddict(Key, Value) = [{Key, Value}]

Dictionary as returned by new/0.

####
orddict() = orddict(term(), term())

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Exports

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append(Key, Value, Orddict1) -> Orddict2

### Types

Orddict1 = Orddict2 = orddict(Key, Value)

Appends a new Value to the current list of values associated with Key. An exception is generated if the initial value associated with Key is not a list of values.

See also section Notes.

Example 1:

    1> OrdDict1 = orddict:from_list([{x, []}]).
    [{x,[]}]
    2> OrdDict2 = orddict:append(x, 1, OrdDict1).
    [{x,[1]}]
    3> OrdDict3 = orddict:append(x, 2, OrdDict2).
    [{x,[1,2]}]
    4> orddict:append(y, 3, OrdDict3).
    [{x,[1,2]},{y,[3]}]

Example 2:

    1> OrdDict1 = orddict:from_list([{a, no_list}]).
    [{a,no_list}]
    2> orddict:append(a, 1, OrdDict1).
    ** exception error: bad argument
         in operator  ++/2
            called as no_list ++ [1]

####
append_list(Key, ValList, Orddict1) -> Orddict2

### Types

ValList = [Value]
Orddict1 = Orddict2 = orddict(Key, Value)

Appends a list of values ValList to the current list of values associated with Key. An exception is generated if the initial value associated with Key is not a list of values.

See also section Notes.

Example:

    1> OrdDict1 = orddict:from_list([{x, []}]).
    [{x,[]}]
    2> OrdDict2 = orddict:append_list(x, [1,2], OrdDict1).
    [{x,[1,2]}]
    3> OrdDict3 = orddict:append_list(y, [3,4], OrdDict2).
    [{x,[1,2]},{y,[3,4]}]

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erase(Key, Orddict1) -> Orddict2

### Types

Orddict1 = Orddict2 = orddict(Key, Value)

Erases all items with a specified key from a dictionary.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:erase(a, OrdDict1).
    [{b,2}]

####
fetch(Key, Orddict) -> Value

### Types

Orddict = orddict(Key, Value)

Returns the value associated with Key in dictionary Orddict. This function assumes that the Key is present in the dictionary. An exception is generated if Key is not in the dictionary.

See also section Notes.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:fetch(a, OrdDict1).
    1
    3> orddict:fetch(missing, OrdDict1).
    ** exception error: no function clause matching orddict:fetch(missing,[])

####
fetch_keys(Orddict) -> Keys

### Types

Orddict = orddict(Key, Value :: term())
Keys = [Key]

Returns a list of all keys in a dictionary.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:fetch_keys(OrdDict1).
    [a,b]

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take(Key, Orddict) -> {Value, Orddict1} | error
OTP 20.0

### Types

Orddict = Orddict1 = orddict(Key, Value)
Key = Value = term()

This function returns value from dictionary and new dictionary without this value. Returns error if the key is not present in the dictionary.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:take(a, OrdDict1).
    {1, [{b,2}]}
    3> orddict:take(missing, OrdDict1).
    error

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filter(Pred, Orddict1) -> Orddict2

### Types

Pred = fun((Key, Value) -> boolean())
Orddict1 = Orddict2 = orddict(Key, Value)

Orddict2 is a dictionary of all keys and values in Orddict1 for which Pred(Key, Value) is true.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:filter(fun (K, V) -> V > 1 end, OrdDict1).
    [{b,2}]

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find(Key, Orddict) -> {ok, Value} | error

### Types

Orddict = orddict(Key, Value)

Searches for a key in a dictionary. Returns {ok, Value}, where Value is the value associated with Key, or error if the key is not present in the dictionary.

See also section Notes.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:find(a, OrdDict1).
    {ok,1}
    3> orddict:find(c, OrdDict1).
    error

####
fold(Fun, Acc0, Orddict) -> Acc1

### Types

Fun = fun((Key, Value, AccIn) -> AccOut)
Orddict = orddict(Key, Value)
Acc0 = Acc1 = AccIn = AccOut = Acc

Calls Fun on successive keys and values of Orddict together with an extra argument Acc (short for accumulator). Fun must return a new accumulator that is passed to the next call. Acc0 is returned if the list is empty.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:fold(fun (K, V, Acc) -> [{K, V+100} | Acc] end, [], OrdDict1).
    [{b,102},{a,101}]

####
from_list(List) -> Orddict

### Types

List = [{Key, Value}]
Orddict = orddict(Key, Value)

Converts the Key-Value list List to a dictionary.

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is_empty(Orddict) -> boolean()
OTP 17.0

### Types

Orddict = orddict()

Returns true if Orddict has no elements, otherwise false.

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is_key(Key, Orddict) -> boolean()

### Types

Orddict = orddict(Key, Value :: term())

Tests if Key is contained in dictionary Orddict.

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map(Fun, Orddict1) -> Orddict2

### Types

Fun = fun((Key, Value1) -> Value2)
Orddict1 = orddict(Key, Value1)
Orddict2 = orddict(Key, Value2)

Calls Fun on successive keys and values of Orddict1 to return a new value for each key.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:map(fun (_K, V) -> V + 100 end, OrdDict1).
    [{a,101},{b,102}]

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merge(Fun, Orddict1, Orddict2) -> Orddict3

### Types

Fun = fun((Key, Value1, Value2) -> Value)
Orddict1 = orddict(Key, Value1)
Orddict2 = orddict(Key, Value2)
Orddict3 = orddict(Key, Value)

Merges two dictionaries, Orddict1 and Orddict2, to create a new dictionary. All the Key-Value pairs from both dictionaries are included in the new dictionary. If a key occurs in both dictionaries, Fun is called with the key and both values to return a new value. merge/3 can be defined as follows, but is faster:

    merge(Fun, D1, D2) ->
        fold(fun (K, V1, D) ->
                     update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
             end, D2, D1).

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> OrdDict2 = orddict:from_list([{b, 7}, {c, 8}]).
    [{b,7},{c,8}]
    3> orddict:merge(fun (K, V1, V2) -> V1 * V2 end, OrdDict1, OrdDict2).
    [{a, 1},{b, 14},{c,8}]

####
new() -> orddict(none(), none())

Creates a new dictionary.

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size(Orddict) -> integer() >= 0

### Types

Orddict = orddict()

Returns the number of elements in an Orddict.

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store(Key, Value, Orddict1) -> Orddict2

### Types

Orddict1 = Orddict2 = orddict(Key, Value)

Stores a Key-Value pair in a dictionary. If the Key already exists in Orddict1, the associated value is replaced by Value.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:store(a, 99, OrdDict1).
    [{a,99},{b,2}]
    3> orddict:store(c, 100, OrdDict1).
    [{a,1},{b,2},{c,100}]

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to_list(Orddict) -> List

### Types

Orddict = orddict(Key, Value)
List = [{Key, Value}]

Converts a dictionary to a list representation.

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update(Key, Fun, Orddict1) -> Orddict2

### Types

Fun = fun((Value1 :: Value) -> Value2 :: Value)
Orddict1 = Orddict2 = orddict(Key, Value)

Updates a value in a dictionary by calling Fun on the value to get a new value. An exception is generated if Key is not present in the dictionary.

Example:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:update(a, fun (V) -> V1 + 100 end, OrdDict1).
    [{a, 101}, {b, 102}]

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update(Key, Fun, Initial, Orddict1) -> Orddict2

### Types

Initial = Value
Fun = fun((Value1 :: Value) -> Value2 :: Value)
Orddict1 = Orddict2 = orddict(Key, Value)

Updates a value in a dictionary by calling Fun on the value to get a new value. If Key is not present in the dictionary, Initial is stored as the first value. For example, append/3 can be defined as follows:

    append(Key, Val, D) ->
        update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).

Example 1:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:update(c, fun (V) -> V1 + 100 end, 99, OrdDict1).
    [{a,1},{b,2},{c,99}]

Example 2:

    1> OrdDict1 = orddict:from_list([{a, 1}, {b, 2}]).
    [{a,1},{b,2}]
    2> orddict:update(a, fun (V) -> V1 + 100 end, 99, OrdDict1).
    [{a,101},{b,2}]

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update_counter(Key, Increment, Orddict1) -> Orddict2

### Types

Orddict1 = Orddict2 = orddict(Key, Value)
Increment = number()

Adds Increment to the value associated with Key and store this value. If Key is not present in the dictionary, Increment is stored as the first value.

This can be defined as follows, but is faster:

    update_counter(Key, Incr, D) ->
        update(Key, fun (Old) -> Old + Incr end, Incr, D).

###
Notes

Functions append/3 and append_list/3 are included so that keyed values can be stored in a list accumulator, for example:

    > D0 = orddict:new(),
      D1 = orddict:store(files, [], D0),
      D2 = orddict:append(files, f1, D1),
      D3 = orddict:append(files, f2, D2),
      D4 = orddict:append(files, f3, D3),
      orddict:fetch(files, D4).
    [f1,f2,f3]

This saves the trouble of first fetching a keyed value, appending a new value to the list of stored values, and storing the result.

Function fetch/2 is to be used if the key is known to be in the dictionary, otherwise function find/2.

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See Also

dict(3), gb_trees(3)