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# array

### MODULE

array

### MODULE SUMMARY

Functional, extendible arrays.

### 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 datastructures, e.g. 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 which has been explicitly set to the same value as the default one (cf. reset/2). If you need to differentiate between unset and set entries, you must make sure 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 successfully to set an entry, all indices in the range [0,I] will 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 the 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)).

### DATA TYPES

array()

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

### EXPORTS

default(Array::array()) -> term()

Get the value used for uninitialized entries.

See also: new/2.

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

Fix the size of the array. This prevents it from growing automatically upon insertion; see also set/3.

See also: relax/1.

foldl(Function, InitialAcc::term(), Array::array()) -> term()

Types:

Function = (Index::integer(), Value::term(), Acc::term()) -> term()

Fold the elements of the array using the given 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.

foldr(Function, InitialAcc::term(), Array::array()) -> term()

Types:

Function = (Index::integer(), Value::term(), Acc::term()) -> term()

Fold the elements of the array right-to-left using the given 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.

from_list(List::list()) -> array()

Equivalent to from_list(List, undefined).

from_list(List::list(), Default::term()) -> array()

Convert 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.

from_orddict(Orddict::list()) -> array()

Equivalent to from_orddict(Orddict, undefined).

from_orddict(List::list(), Default::term()) -> array()

Convert 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 List is not a proper, ordered list of pairs whose first elements are nonnegative integers, the call fails with reason badarg.

See also: new/2, to_orddict/1.

get(I::integer(), Array::array()) -> term()

Get the value of entry I. If I is not a nonnegative 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, this function will return the default value for any index I greater than size(Array)-1.

See also: set/3.

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

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

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

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

See also: fix/1.

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

Types:

Function = (Index::integer(), Value::term()) -> term()

Map the given function onto each element of the array. 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.

new() -> array()

Create a new, extendible array with initial size zero.

See also: new/1, new/2.

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

Create a new array according to the given options. 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() or {size, N::integer()}

  Specifies the initial size of the array; this also implies {fixed, true}. If N is not a nonnegative 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, i.e., 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.

new(Size::integer(), Options::term()) -> array()

Create a new array according to the given size and options. If Size is not a nonnegative integer, the call fails with reason badarg. By default, the array has fixed size. Note that any size specifications in Options will override the Size parameter.

If Options is a list, this is simply 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.

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

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

See also: fix/1.

reset(I::integer(), Array::array()) -> array()

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

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

See also: new/2, set/3.

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

Change the size of the array to that reported by sparse_size/1. If the given array has fixed size, the resulting array will also have fixed size.

See also: resize/2, sparse_size/1.

resize(Size::integer(), Array::array()) -> array()

Change the size of the array. If Size is not a nonnegative integer, the call fails with reason badarg. If the given array has fixed size, the resulting array will also have fixed size.

set(I::integer(), Value::term(), Array::array()) -> array()

Set entry I of the array to Value. If I is not a nonnegative 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 will grow to size I+1.

See also: get/2, reset/2.

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

Get 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.

sparse_foldl(Function, InitialAcc::term(), Array::array()) -> term()

Types:

Function = (Index::integer(), Value::term(), Acc::term()) -> term()

Fold the elements of the array using the given 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.

sparse_foldr(Function, InitialAcc::term(), Array::array()) -> term()

Types:

Function = (Index::integer(), Value::term(), Acc::term()) -> term()

Fold the elements of the array right-to-left using the given 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.

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

Types:

Function = (Index::integer(), Value::term()) -> term()

Map the given function onto each element of the array, 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.

sparse_size(A::array()) -> integer()

Get the number of entries in the array up until the last non-default valued entry. In other words, 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.

sparse_to_list(Array::array()) -> list()

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

See also: to_list/1.

sparse_to_orddict(Array::array()) -> [{Index::integer(), Value::term()}]

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

See also: to_orddict/1.

to_list(Array::array()) -> list()

Converts the array to a list.

See also: from_list/2, sparse_to_list/1.

to_orddict(Array::array()) -> [{Index::integer(), Value::term()}]

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

See also: from_orddict/2, sparse_to_orddict/1.