path: root/lib/stdlib/doc/src/array.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
    <copyright>
      <year>2007</year><year>2014</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
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<title>array</title>
<prepared></prepared>
<responsible></responsible>
<docno>1</docno>
<approved></approved>
<checked></checked>
<date></date>
<rev>A</rev>
<file>array.xml</file></header>
<module>array</module>
<modulesummary>Functional, extendible arrays.</modulesummary>
<description>
<p>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.</p>
 
  <p>Arrays uses <em>zero</em> based indexing. This is a deliberate design  
choice and differs from other erlang datastructures, e.g. tuples.</p>
 
  <p>Unless specified by the user when the array is created, the default
  value is the atom <c>undefined</c>. 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. <seealso marker="#reset-2">reset/2</seealso>). 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.</p>
 
  <p>The array never shrinks automatically; if an index <c>I</c> has been used
  successfully to set an entry, all indices in the range [0,<c>I</c>] will
  stay accessible unless the array size is explicitly changed by
  calling <seealso marker="#resize-2">resize/2</seealso>.</p>
 
  <p>Examples:
  </p><pre>  %% 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)).</pre></description>
<datatypes>
  <datatype>
    <name name="array" n_vars="1"/>
    <desc>
      <p>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.</p>
    </desc>
  </datatype>
  <datatype>
    <name name="array" n_vars="0"/>
  </datatype>
  <datatype>
    <name name="array_indx"/>
  </datatype>
  <datatype>
    <name name="array_opts"/>
  </datatype>
  <datatype>
    <name name="array_opt"/>
  </datatype>
  <datatype>
    <name name="indx_pairs"/>
  </datatype>
  <datatype>
    <name name="indx_pair"/>
  </datatype>
</datatypes>

<funcs>
<func>
<name name="default" arity="1"/>
<fsummary>Get the value used for uninitialized entries.</fsummary>

<desc><marker id="default-1"/>

<p>Get the value used for uninitialized entries.
 </p>
<p><em>See also:</em> <seealso marker="#new-2">new/2</seealso>.</p>
</desc></func>
<func>
<name name="fix" arity="1"/>
<fsummary>Fix the size of the array.</fsummary>

<desc><marker id="fix-1"/>

<p>Fix the size of the array. This prevents it from growing
  automatically upon insertion; see also <seealso marker="#set-3">set/3</seealso>.</p>
<p><em>See also:</em> <seealso marker="#relax-1">relax/1</seealso>.</p>
</desc></func>
<func>
<name name="foldl" arity="3"/>
<fsummary>Fold the elements of the array using the given function and
  initial accumulator value.</fsummary>
<desc><marker id="foldl-3"/>
<p>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 <c><anno>Function</anno></c> is not a function, the
  call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#foldr-3">foldr/3</seealso>, <seealso marker="#map-2">map/2</seealso>, <seealso marker="#sparse_foldl-3">sparse_foldl/3</seealso>.</p>
</desc></func>
<func>
<name name="foldr" arity="3"/>
<fsummary>Fold the elements of the array right-to-left using the given
  function and initial accumulator value.</fsummary>
<desc><marker id="foldr-3"/>

<p>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 <c><anno>Function</anno></c> is not a
  function, the call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#foldl-3">foldl/3</seealso>, <seealso marker="#map-2">map/2</seealso>.</p>
</desc></func>
<func>
<name name="from_list" arity="1"/>
<fsummary>Equivalent to from_list(List, undefined).
</fsummary>

<desc><marker id="from_list-1"/>
<p>Equivalent to <seealso marker="#from_list-2">from_list(<anno>List</anno>, undefined)</seealso>.</p>
</desc></func>
<func>
<name name="from_list" arity="2"/>
<fsummary>Convert a list to an extendible array.</fsummary>

<desc><marker id="from_list-2"/>

<p>Convert a list to an extendible array. <c><anno>Default</anno></c> is used as the value
  for uninitialized entries of the array. If <c><anno>List</anno></c> is not a proper list,
  the call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#new-2">new/2</seealso>, <seealso marker="#to_list-1">to_list/1</seealso>.</p>
</desc></func>
<func>
<name name="from_orddict" arity="1"/>
<fsummary>Equivalent to from_orddict(Orddict, undefined).
</fsummary>

<desc><marker id="from_orddict-1"/>
<p>Equivalent to <seealso marker="#from_orddict-2">from_orddict(<anno>Orddict</anno>, undefined)</seealso>.</p>
</desc></func>
<func>
<name name="from_orddict" arity="2"/>
<fsummary>Convert an ordered list of pairs {Index, Value} to a
  corresponding extendible array.</fsummary>

<desc><marker id="from_orddict-2"/>

<p>Convert an ordered list of pairs <c>{Index, <anno>Value</anno>}</c> to a
  corresponding extendible array. <c><anno>Default</anno></c> is used as the value for
  uninitialized entries of the array. If <c><anno>Orddict</anno></c> is not a proper,
  ordered list of pairs whose first elements are nonnegative
  integers, the call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#new-2">new/2</seealso>, <seealso marker="#to_orddict-1">to_orddict/1</seealso>.</p>
</desc></func>
<func>
<name name="get" arity="2"/>
<fsummary>Get the value of entry I.</fsummary>

<desc><marker id="get-2"/>

<p>Get the value of entry <c><anno>I</anno></c>. If <c><anno>I</anno></c> is not a nonnegative
  integer, or if the array has fixed size and <c><anno>I</anno></c> is larger than the
  maximum index, the call fails with reason <c>badarg</c>.</p>
 
  <p>If the array does not have fixed size, this function will return the
  default value for any index <c><anno>I</anno></c> greater than <c>size(<anno>Array</anno>)-1</c>.</p>
<p><em>See also:</em> <seealso marker="#set-3">set/3</seealso>.</p>
</desc></func>
<func>
<name name="is_array" arity="1"/>
<fsummary>Returns true if X appears to be an array, otherwise false.</fsummary>

<desc><marker id="is_array-1"/>

<p>Returns <c>true</c> if <c><anno>X</anno></c> appears to be an array, otherwise <c>false</c>.
  Note that the check is only shallow; there is no guarantee that <c><anno>X</anno></c>
  is a well-formed array representation even if this function returns
  <c>true</c>.</p>
</desc></func>
<func>
<name name="is_fix" arity="1"/>
<fsummary>Check if the array has fixed size.</fsummary>

<desc><marker id="is_fix-1"/>

<p>Check if the array has fixed size.
  Returns <c>true</c> if the array is fixed, otherwise <c>false</c>.</p>
<p><em>See also:</em> <seealso marker="#fix-1">fix/1</seealso>.</p>
</desc></func>
<func>
<name name="map" arity="2"/>
<fsummary>Map the given function onto each element of the array.</fsummary>
<desc><marker id="map-2"/>

<p>Map the given function onto each element of the array. The
  elements are visited in order from the lowest index to the highest.
  If <c><anno>Function</anno></c> is not a function, the call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#foldl-3">foldl/3</seealso>, <seealso marker="#foldr-3">foldr/3</seealso>, <seealso marker="#sparse_map-2">sparse_map/2</seealso>.</p>
</desc></func>
<func>
<name name="new" arity="0"/>
<fsummary>Create a new, extendible array with initial size zero.</fsummary>

<desc><marker id="new-0"/>

<p>Create a new, extendible array with initial size zero.</p>
<p><em>See also:</em> <seealso marker="#new-1">new/1</seealso>, <seealso marker="#new-2">new/2</seealso>.</p>
</desc></func>
<func>
<name name="new" arity="1"/>
<fsummary>Create a new array according to the given options.</fsummary>

<desc><marker id="new-1"/>

<p>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.</p>
 
  <p><c><anno>Options</anno></c> is a single term or a list of terms, selected from the
  following:
  </p><taglist>
    <tag><c>N::integer() >= 0</c> or <c>{size, N::integer() >= 0}</c></tag>
    <item><p>Specifies the initial size of the array; this also implies
    <c>{fixed, true}</c>. If <c>N</c> is not a nonnegative integer, the call
    fails with reason <c>badarg</c>.</p></item>
    <tag><c>fixed</c> or <c>{fixed, true}</c></tag>
    <item><p>Creates a fixed-size array; see also <seealso marker="#fix-1">fix/1</seealso>.</p></item>
    <tag><c>{fixed, false}</c></tag>
    <item><p>Creates an extendible (non fixed-size) array.</p></item>
    <tag><c>{default, Value}</c></tag>
    <item><p>Sets the default value for the array to <c>Value</c>.</p></item>
  </taglist><p>  
Options are processed in the order they occur in the list, i.e.,  
later options have higher precedence.</p>
 
  <p>The default value is used as the value of uninitialized entries, and  
cannot be changed once the array has been created.</p>
 
  <p>Examples:
  </p><pre>     array:new(100)</pre><p> creates a fixed-size array of size 100.
  </p><pre>     array:new({default,0})</pre><p> creates an empty, extendible array
  whose default value is 0.
  </p><pre>     array:new([{size,10},{fixed,false},{default,-1}])</pre><p> creates an
  extendible array with initial size 10 whose default value is -1.
 </p>
<p><em>See also:</em> <seealso marker="#fix-1">fix/1</seealso>, <seealso marker="#from_list-2">from_list/2</seealso>, <seealso marker="#get-2">get/2</seealso>, <seealso marker="#new-0">new/0</seealso>, <seealso marker="#new-2">new/2</seealso>, <seealso marker="#set-3">set/3</seealso>.</p>
</desc></func>
<func>
<name name="new" arity="2"/>
<fsummary>Create a new array according to the given size and options.</fsummary>

<desc><marker id="new-2"/>

<p>Create a new array according to the given size and options. If
  <c><anno>Size</anno></c> is not a nonnegative integer, the call fails with reason
  <c>badarg</c>. By default, the array has fixed size. Note that any size
  specifications in <c><anno>Options</anno></c> will override the <c><anno>Size</anno></c> parameter.</p>
 
  <p>If <c><anno>Options</anno></c> is a list, this is simply equivalent to <c>new([{size,
  <anno>Size</anno>} | <anno>Options</anno>]</c>, otherwise it is equivalent to <c>new([{size, <anno>Size</anno>} |
  [<anno>Options</anno>]]</c>. However, using this function directly is more efficient.</p>
 
  <p>Example:
  </p><pre>     array:new(100, {default,0})</pre><p> creates a fixed-size array of size
  100, whose default value is 0.
 </p>
<p><em>See also:</em> <seealso marker="#new-1">new/1</seealso>.</p>
</desc></func>
<func>
<name name="relax" arity="1"/>
<fsummary>Make the array resizable.</fsummary>

<desc><marker id="relax-1"/>

<p>Make the array resizable. (Reverses the effects of <seealso marker="#fix-1">fix/1</seealso>.)</p>
<p><em>See also:</em> <seealso marker="#fix-1">fix/1</seealso>.</p>
</desc></func>
<func>
<name name="reset" arity="2"/>
<fsummary>Reset entry I to the default value for the array.</fsummary>

<desc><marker id="reset-2"/>

<p>Reset entry <c><anno>I</anno></c> to the default value for the array.
  If the value of entry <c><anno>I</anno></c> 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 <seealso marker="#resize-2">resize/2</seealso>.</p>
 
  <p>If <c><anno>I</anno></c> is not a nonnegative integer, or if the array has fixed size
  and <c><anno>I</anno></c> is larger than the maximum index, the call fails with reason
  <c>badarg</c>; cf. <seealso marker="#set-3">set/3</seealso>
 </p>
<p><em>See also:</em> <seealso marker="#new-2">new/2</seealso>, <seealso marker="#set-3">set/3</seealso>.</p>
</desc></func>
<func>
<name name="resize" arity="1"/>
<fsummary>Change the size of the array to that reported by sparse_size/1.</fsummary>

<desc><marker id="resize-1"/>

<p>Change the size of the array to that reported by <seealso marker="#sparse_size-1">sparse_size/1</seealso>. If the given array has fixed size, the resulting
  array will also have fixed size.</p>
<p><em>See also:</em> <seealso marker="#resize-2">resize/2</seealso>, <seealso marker="#sparse_size-1">sparse_size/1</seealso>.</p>
</desc></func>
<func>
<name name="resize" arity="2"/>
<fsummary>Change the size of the array.</fsummary>

<desc><marker id="resize-2"/>

<p>Change the size of the array. If <c><anno>Size</anno></c> is not a nonnegative
  integer, the call fails with reason <c>badarg</c>. If the given array has
  fixed size, the resulting array will also have fixed size.</p>
</desc></func>
<func>
<name name="set" arity="3"/>
<fsummary>Set entry I of the array to Value.</fsummary>

<desc><marker id="set-3"/>

<p>Set entry <c><anno>I</anno></c> of the array to <c><anno>Value</anno></c>. If <c><anno>I</anno></c> is not a
  nonnegative integer, or if the array has fixed size and <c><anno>I</anno></c> is larger
  than the maximum index, the call fails with reason <c>badarg</c>.</p>
 
  <p>If the array does not have fixed size, and <c><anno>I</anno></c> is greater than
  <c>size(<anno>Array</anno>)-1</c>, the array will grow to size <c><anno>I</anno>+1</c>.
 </p>
<p><em>See also:</em> <seealso marker="#get-2">get/2</seealso>, <seealso marker="#reset-2">reset/2</seealso>.</p>
</desc></func>
<func>
<name name="size" arity="1"/>
<fsummary>Get the number of entries in the array.</fsummary>

<desc><marker id="size-1"/>

<p>Get the number of entries in the array. Entries are numbered
  from 0 to <c>size(<anno>Array</anno>)-1</c>; hence, this is also the index of the first
  entry that is guaranteed to not have been previously set.</p>
<p><em>See also:</em> <seealso marker="#set-3">set/3</seealso>, <seealso marker="#sparse_size-1">sparse_size/1</seealso>.</p>
</desc></func>
<func>
<name name="sparse_foldl" arity="3"/>
<fsummary>Fold the elements of the array using the given function and
  initial accumulator value, skipping default-valued entries.</fsummary>
<desc><marker id="sparse_foldl-3"/>

<p>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 <c><anno>Function</anno></c> is not a function, the call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#foldl-3">foldl/3</seealso>, <seealso marker="#sparse_foldr-3">sparse_foldr/3</seealso>.</p>
</desc></func>
<func>
<name name="sparse_foldr" arity="3"/>
<fsummary>Fold the elements of the array right-to-left using the given
  function and initial accumulator value, skipping default-valued
  entries.</fsummary>
<desc><marker id="sparse_foldr-3"/>

<p>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 <c><anno>Function</anno></c> is not a function, the call fails with
  reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#foldr-3">foldr/3</seealso>, <seealso marker="#sparse_foldl-3">sparse_foldl/3</seealso>.</p>
</desc></func>
<func>
<name name="sparse_map" arity="2"/>
<fsummary>Map the given function onto each element of the array, skipping
  default-valued entries.</fsummary>
<desc><marker id="sparse_map-2"/>

<p>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 <c><anno>Function</anno></c> is not a function, the
  call fails with reason <c>badarg</c>.
 </p>
<p><em>See also:</em> <seealso marker="#map-2">map/2</seealso>.</p>
</desc></func>
<func>
<name name="sparse_size" arity="1"/>
<fsummary>Get the number of entries in the array up until the last
  non-default valued entry.</fsummary>

<desc><marker id="sparse_size-1"/>

<p>Get the number of entries in the array up until the last
  non-default valued entry. In other words, returns <c>I+1</c> if <c>I</c> is the
  last non-default valued entry in the array, or zero if no such entry
  exists.</p>
<p><em>See also:</em> <seealso marker="#resize-1">resize/1</seealso>, <seealso marker="#size-1">size/1</seealso>.</p>
</desc></func>
<func>
<name name="sparse_to_list" arity="1"/>
<fsummary>Converts the array to a list, skipping default-valued entries.</fsummary>

<desc><marker id="sparse_to_list-1"/>

<p>Converts the array to a list, skipping default-valued entries.
 </p>
<p><em>See also:</em> <seealso marker="#to_list-1">to_list/1</seealso>.</p>
</desc></func>
<func>
<name name="sparse_to_orddict" arity="1"/>
<fsummary>Convert the array to an ordered list of pairs {Index, Value},
  skipping default-valued entries.</fsummary>

<desc><marker id="sparse_to_orddict-1"/>

<p>Convert the array to an ordered list of pairs <c>{Index, <anno>Value</anno>}</c>,
  skipping default-valued entries.
 </p>
<p><em>See also:</em> <seealso marker="#to_orddict-1">to_orddict/1</seealso>.</p>
</desc></func>
<func>
<name name="to_list" arity="1"/>
<fsummary>Converts the array to a list.</fsummary>

<desc><marker id="to_list-1"/>

<p>Converts the array to a list.
 </p>
<p><em>See also:</em> <seealso marker="#from_list-2">from_list/2</seealso>, <seealso marker="#sparse_to_list-1">sparse_to_list/1</seealso>.</p>
</desc></func>
<func>
<name name="to_orddict" arity="1"/>
<fsummary>Convert the array to an ordered list of pairs {Index, Value}.</fsummary>

<desc><marker id="to_orddict-1"/>

<p>Convert the array to an ordered list of pairs <c>{Index, <anno>Value</anno>}</c>.
 </p>
<p><em>See also:</em> <seealso marker="#from_orddict-2">from_orddict/2</seealso>, <seealso marker="#sparse_to_orddict-1">sparse_to_orddict/1</seealso>.</p>
</desc></func></funcs>

</erlref>