# array

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Module

array

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Module Summary

Functional, extendible arrays.

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Description

Functional, extendible arrays. Arrays can have fixed size, or can grow automatically as needed. A default value is used for entries that have not been explicitly set.

Arrays uses zero-based indexing. This is a deliberate design choice and differs from other Erlang data structures, for example, tuples.

Unless specified by the user when the array is created, the default value is the atom undefined. There is no difference between an unset entry and an entry that has been explicitly set to the same value as the default one (compare reset/2). If you need to differentiate between unset and set entries, ensure that the default value cannot be confused with the values of set entries.

The array never shrinks automatically. If an index I has been used to set an entry successfully, all indices in the range [0,I] stay accessible unless the array size is explicitly changed by calling resize/2.

Examples:

Create a fixed-size array with entries 0-9 set to undefined:

    A0 = array:new(10).
    10 = array:size(A0).

Create an extendible array and set entry 17 to true, causing the array to grow automatically:

    A1 = array:set(17, true, array:new()).
    18 = array:size(A1).

Read back a stored value:

    true = array:get(17, A1).

Accessing an unset entry returns default value:

    undefined = array:get(3, A1)

Accessing an entry beyond the last set entry also returns the default value, if the array does not have fixed size:

    undefined = array:get(18, A1).

"Sparse" functions ignore default-valued entries:

    A2 = array:set(4, false, A1).
    [{4, false}, {17, true}] = array:sparse_to_orddict(A2).

An extendible array can be made fixed-size later:

    A3 = array:fix(A2).

A fixed-size array does not grow automatically and does not allow accesses beyond the last set entry:

    {'EXIT',{badarg,_}} = (catch array:set(18, true, A3)).
    {'EXIT',{badarg,_}} = (catch array:get(18, A3)).

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Data Types

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array(Type)

A functional, extendible array. The representation is not documented and is subject to change without notice. Notice that arrays cannot be directly compared for equality.

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array() = array(term())

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array_indx() = integer() >= 0

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array_opts() = array_opt() | [array_opt()]

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array_opt() =
{fixed, boolean()} |
fixed |
{default, Type :: term()} |
{size, N :: integer() >= 0} |
(N :: integer() >= 0)

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indx_pairs(Type) = [indx_pair(Type)]

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indx_pair(Type) = {Index :: array_indx(), Type}

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Exports

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default(Array :: array(Type)) -> Value :: Type

Gets the value used for uninitialized entries.

See also new/2.

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fix(Array :: array(Type)) -> array(Type)

Fixes the array size. This prevents it from growing automatically upon insertion.

See also set/3 and relax/1.

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foldl(Function, InitialAcc :: A, Array :: array(Type)) -> B

### Types

Function =
fun((Index :: array_indx(), Value :: Type, Acc :: A) -> B)

Folds the array elements using the specified function and initial accumulator value. The elements are visited in order from the lowest index to the highest. If Function is not a function, the call fails with reason badarg.

See also foldr/3, map/2, sparse_foldl/3.

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foldr(Function, InitialAcc :: A, Array :: array(Type)) -> B

### Types

Function =
fun((Index :: array_indx(), Value :: Type, Acc :: A) -> B)

Folds the array elements right-to-left using the specified function and initial accumulator value. The elements are visited in order from the highest index to the lowest. If Function is not a function, the call fails with reason badarg.

See also foldl/3, map/2.

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from_list(List :: [Value :: Type]) -> array(Type)

Equivalent to from_list(List, undefined).

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from_list(List :: [Value :: Type], Default :: term()) ->
array(Type)

Converts a list to an extendible array. Default is used as the value for uninitialized entries of the array. If List is not a proper list, the call fails with reason badarg.

See also new/2, to_list/1.

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from_orddict(Orddict :: indx_pairs(Value :: Type)) -> array(Type)

Equivalent to from_orddict(Orddict, undefined).

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from_orddict(Orddict :: indx_pairs(Value :: Type),
Default :: Type) ->
array(Type)

Converts an ordered list of pairs {Index, Value} to a corresponding extendible array. Default is used as the value for uninitialized entries of the array. If Orddict is not a proper, ordered list of pairs whose first elements are non-negative integers, the call fails with reason badarg.

See also new/2, to_orddict/1.

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get(I :: array_indx(), Array :: array(Type)) -> Value :: Type

Gets the value of entry I. If I is not a non-negative integer, or if the array has fixed size and I is larger than the maximum index, the call fails with reason badarg.

If the array does not have fixed size, the default value for any index I greater than size(Array)-1 is returned.

See also set/3.

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is_array(X :: term()) -> boolean()

Returns true if X is an array, otherwise false. Notice that the check is only shallow, as there is no guarantee that X is a well-formed array representation even if this function returns true.

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is_fix(Array :: array()) -> boolean()

Checks if the array has fixed size. Returns true if the array is fixed, otherwise false.

See also fix/1.

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map(Function, Array :: array(Type1)) -> array(Type2)

### Types

Function = fun((Index :: array_indx(), Type1) -> Type2)

Maps the specified function onto each array element. The elements are visited in order from the lowest index to the highest. If Function is not a function, the call fails with reason badarg.

See also foldl/3, foldr/3, sparse_map/2.

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new() -> array()

Creates a new, extendible array with initial size zero.

See also new/1, new/2.

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new(Options :: array_opts()) -> array()

Creates a new array according to the specified otions. By default, the array is extendible and has initial size zero. Array indices start at 0.

Options is a single term or a list of terms, selected from the following:

N::integer() >= 0 or {size, N::integer() >= 0}

  Specifies the initial array size; this also implies {fixed, true}. If N is not a non-negative integer, the call fails with reason badarg.

fixed or {fixed, true}

  Creates a fixed-size array. See also fix/1.

{fixed, false}

  Creates an extendible (non-fixed-size) array.

{default, Value}

  Sets the default value for the array to Value.

Options are processed in the order they occur in the list, that is, later options have higher precedence.

The default value is used as the value of uninitialized entries, and cannot be changed once the array has been created.

Examples:

    array:new(100)

creates a fixed-size array of size 100.

    array:new({default,0})

creates an empty, extendible array whose default value is 0.

    array:new([{size,10},{fixed,false},{default,-1}])

creates an extendible array with initial size 10 whose default value is -1.

See also fix/1, from_list/2, get/2, new/0, new/2, set/3.

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new(Size :: integer() >= 0, Options :: array_opts()) -> array()

Creates a new array according to the specified size and options. If Size is not a non-negative integer, the call fails with reason badarg. By default, the array has fixed size. Notice that any size specifications in Options override parameter Size.

If Options is a list, this is equivalent to new([{size, Size} | Options]), otherwise it is equivalent to new([{size, Size} | [Options]]). However, using this function directly is more efficient.

Example:

    array:new(100, {default,0})

creates a fixed-size array of size 100, whose default value is 0.

See also new/1.

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relax(Array :: array(Type)) -> array(Type)

Makes the array resizable. (Reverses the effects of fix/1.)

See also fix/1.

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reset(I :: array_indx(), Array :: array(Type)) -> array(Type)

Resets entry I to the default value for the array. If the value of entry I is the default value, the array is returned unchanged. Reset never changes the array size. Shrinking can be done explicitly by calling resize/2.

If I is not a non-negative integer, or if the array has fixed size and I is larger than the maximum index, the call fails with reason badarg; compare set/3

See also new/2, set/3.

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resize(Array :: array(Type)) -> array(Type)

Changes the array size to that reported by sparse_size/1. If the specified array has fixed size, also the resulting array has fixed size.

See also resize/2, sparse_size/1.

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resize(Size :: integer() >= 0, Array :: array(Type)) ->
array(Type)

Change the array size. If Size is not a non-negative integer, the call fails with reason badarg. If the specified array has fixed size, also the resulting array has fixed size.

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set(I :: array_indx(), Value :: Type, Array :: array(Type)) ->
array(Type)

Sets entry I of the array to Value. If I is not a non-negative integer, or if the array has fixed size and I is larger than the maximum index, the call fails with reason badarg.

If the array does not have fixed size, and I is greater than size(Array)-1, the array grows to size I+1.

See also get/2, reset/2.

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size(Array :: array()) -> integer() >= 0

Gets the number of entries in the array. Entries are numbered from 0 to size(Array)-1. Hence, this is also the index of the first entry that is guaranteed to not have been previously set.

See also set/3, sparse_size/1.

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sparse_foldl(Function, InitialAcc :: A, Array :: array(Type)) -> B

### Types

Function =
fun((Index :: array_indx(), Value :: Type, Acc :: A) -> B)

Folds the array elements using the specified function and initial accumulator value, skipping default-valued entries. The elements are visited in order from the lowest index to the highest. If Function is not a function, the call fails with reason badarg.

See also foldl/3, sparse_foldr/3.

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sparse_foldr(Function, InitialAcc :: A, Array :: array(Type)) -> B

### Types

Function =
fun((Index :: array_indx(), Value :: Type, Acc :: A) -> B)

Folds the array elements right-to-left using the specified function and initial accumulator value, skipping default-valued entries. The elements are visited in order from the highest index to the lowest. If Function is not a function, the call fails with reason badarg.

See also foldr/3, sparse_foldl/3.

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sparse_map(Function, Array :: array(Type1)) -> array(Type2)

### Types

Function = fun((Index :: array_indx(), Type1) -> Type2)

Maps the specified function onto each array element, skipping default-valued entries. The elements are visited in order from the lowest index to the highest. If Function is not a function, the call fails with reason badarg.

See also map/2.

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sparse_size(Array :: array()) -> integer() >= 0

Gets the number of entries in the array up until the last non-default-valued entry. That is, returns I+1 if I is the last non-default-valued entry in the array, or zero if no such entry exists.

See also resize/1, size/1.

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sparse_to_list(Array :: array(Type)) -> [Value :: Type]

Converts the array to a list, skipping default-valued entries.

See also to_list/1.

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sparse_to_orddict(Array :: array(Type)) ->
indx_pairs(Value :: Type)

Converts the array to an ordered list of pairs {Index, Value}, skipping default-valued entries.

See also to_orddict/1.

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to_list(Array :: array(Type)) -> [Value :: Type]

Converts the array to a list.

See also from_list/2, sparse_to_list/1.

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to_orddict(Array :: array(Type)) -> indx_pairs(Value :: Type)

Converts the array to an ordered list of pairs {Index, Value}.

See also from_orddict/2, sparse_to_orddict/1.