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>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <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 data structures, for example,
      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 that has been explicitly set to the same value
      as the default one (compare
      <seealso marker="#reset-2"><c>reset/2</c></seealso>). If you need to
      differentiate between unset and set entries, ensure 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
      to set an entry successfully, all indices in the range [0,<c>I</c>] stay
      accessible unless the array size is explicitly changed by calling
      <seealso marker="#resize-2"><c>resize/2</c></seealso>.</p>

    <p><em>Examples:</em></p>

    <p>Create a fixed-size array with entries 0-9 set to <c>undefined</c>:</p>

    <pre>
A0 = array:new(10).
10 = array:size(A0).</pre>

    <p>Create an extendible array and set entry 17 to <c>true</c>, causing the
      array to grow automatically:</p>

    <pre>
A1 = array:set(17, true, array:new()).
18 = array:size(A1).</pre>

    <p>Read back a stored value:</p>

    <pre>
true = array:get(17, A1).</pre>

    <p>Accessing an unset entry returns default value:</p>

    <pre>
undefined = array:get(3, A1)</pre>

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

    <pre>
undefined = array:get(18, A1).</pre>

    <p>"Sparse" functions ignore default-valued entries:</p>

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

    <p>An extendible array can be made fixed-size later:</p>

    <pre>
A3 = array:fix(A2).</pre>

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

    <pre>
{'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. Notice 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>Gets the value used for uninitialized entries.</p>
        <p>See also <seealso marker="#new-2"><c>new/2</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="fix" arity="1"/>
      <fsummary>Fix the array size.</fsummary>
      <desc><marker id="fix-1"/>
        <p>Fixes the array size. This prevents it from growing automatically
          upon insertion.</p>
        <p>See also <seealso marker="#set-3"><c>set/3</c></seealso> and
          <seealso marker="#relax-1"><c>relax/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="foldl" arity="3"/>
      <fsummary>Fold the array elements using the specified function and initial
        accumulator value.</fsummary>
      <desc><marker id="foldl-3"/>
        <p>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 <c><anno>Function</anno></c> is not a
          function, the call fails with reason <c>badarg</c>.</p>
        <p>See also <seealso marker="#foldr-3"><c>foldr/3</c></seealso>,
          <seealso marker="#map-2"><c>map/2</c></seealso>,
          <seealso marker="#sparse_foldl-3"><c>sparse_foldl/3</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="foldr" arity="3"/>
      <fsummary>Fold the array elements right-to-left using the specified
        function and initial accumulator value.</fsummary>
      <desc><marker id="foldr-3"/>
        <p>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 <c><anno>Function</anno></c> is
          not a function, the call fails with reason <c>badarg</c>.</p>
        <p>See also <seealso marker="#foldl-3"><c>foldl/3</c></seealso>,
          <seealso marker="#map-2"><c>map/2</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="from_list" arity="1"/>
      <fsummary>Equivalent to <c>from_list(List, undefined)</c>.</fsummary>
      <desc><marker id="from_list-1"/>
        <p>Equivalent to
          <seealso marker="#from_list-2"><c>from_list(<anno>List</anno>, undefined)</c></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>Converts 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>See also <seealso marker="#new-2"><c>new/2</c></seealso>,
          <seealso marker="#to_list-1"><c>to_list/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="from_orddict" arity="1"/>
      <fsummary>Equivalent to <c>from_orddict(Orddict, undefined)</c>.
      </fsummary>
      <desc><marker id="from_orddict-1"/>
        <p>Equivalent to
          <seealso marker="#from_orddict-2"><c>from_orddict(<anno>Orddict</anno>, undefined)</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="from_orddict" arity="2"/>
      <fsummary>Convert an ordered list of pairs <c>{Index, Value}</c> to a
        corresponding extendible array.</fsummary>
      <desc><marker id="from_orddict-2"/>
        <p>Converts 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 non-negative integers, the call fails with
          reason <c>badarg</c>.</p>
        <p>See also <seealso marker="#new-2"><c>new/2</c></seealso>,
          <seealso marker="#to_orddict-1"><c>to_orddict/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="get" arity="2"/>
      <fsummary>Get the value of entry <c>I</c>.</fsummary>
      <desc><marker id="get-2"/>
        <p>Gets the value of entry <c><anno>I</anno></c>. If
          <c><anno>I</anno></c> is not a non-negative 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, the default value for any
          index <c><anno>I</anno></c> greater than
          <c>size(<anno>Array</anno>)-1</c> is returned.</p>
        <p>See also <seealso marker="#set-3"><c>set/3</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="is_array" arity="1"/>
      <fsummary>Returns <c>true</c> if <c>X</c> is an array, otherwise
        <c>false</c>.</fsummary>
      <desc><marker id="is_array-1"/>
        <p>Returns <c>true</c> if <c><anno>X</anno></c> is an array, otherwise
          <c>false</c>. Notice that the check is only shallow, as 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>Checks if the array has fixed size. Returns <c>true</c> if the array
          is fixed, otherwise <c>false</c>.</p>
        <p>See also <seealso marker="#fix-1"><c>fix/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="map" arity="2"/>
      <fsummary>Map the specified function onto each array element.</fsummary>
      <desc><marker id="map-2"/>
        <p>Maps the specified function onto each array element. 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>See also <seealso marker="#foldl-3"><c>foldl/3</c></seealso>,
          <seealso marker="#foldr-3"><c>foldr/3</c></seealso>,
          <seealso marker="#sparse_map-2"><c>sparse_map/2</c></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>Creates a new, extendible array with initial size zero.</p>
        <p>See also <seealso marker="#new-1"><c>new/1</c></seealso>,
          <seealso marker="#new-2"><c>new/2</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="new" arity="1"/>
      <fsummary>Create a new array according to the specified options.
      </fsummary>
      <desc><marker id="new-1"/>
        <p>Creates a new array according to the specified otions. By default,
          the array is extendible and has initial size zero. Array indices
          start at <c>0</c>.</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 array size; this also implies
            <c>{fixed, true}</c>. If <c>N</c> is not a non-negative 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"><c>fix/1</c></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, that is,
          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><em>Examples:</em></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 <c>0</c>.
        </p>
        <pre>
array:new([{size,10},{fixed,false},{default,-1}])</pre>
        <p>creates an extendible array with initial size 10 whose default value
          is <c>-1</c>.</p>
        <p>See also <seealso marker="#fix-1"><c>fix/1</c></seealso>,
          <seealso marker="#from_list-2"><c>from_list/2</c></seealso>,
          <seealso marker="#get-2"><c>get/2</c></seealso>,
          <seealso marker="#new-0"><c>new/0</c></seealso>,
          <seealso marker="#new-2"><c>new/2</c></seealso>,
          <seealso marker="#set-3"><c>set/3</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="new" arity="2"/>
      <fsummary>Create a new array according to the specified size and options.
      </fsummary>
      <desc><marker id="new-2"/>
        <p>Creates a new array according to the specified size and options. If
          <c><anno>Size</anno></c> is not a non-negative integer, the call fails
          with reason <c>badarg</c>. By default, the array has fixed size.
          Notice that any size specifications in <c><anno>Options</anno></c>
          override parameter <c><anno>Size</anno></c>.</p>
        <p>If <c><anno>Options</anno></c> is a list, this is 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><em>Example:</em></p>
        <pre>
array:new(100, {default,0})</pre>
        <p>creates a fixed-size array of size 100, whose default value is
          <c>0</c>.</p>
        <p>See also <seealso marker="#new-1"><c>new/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="relax" arity="1"/>
      <fsummary>Make the array resizable.</fsummary>
      <desc><marker id="relax-1"/>
        <p>Makes the array resizable. (Reverses the effects of
          <seealso marker="#fix-1"><c>fix/1</c></seealso>.)</p>
        <p>See also <seealso marker="#fix-1"><c>fix/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="reset" arity="2"/>
      <fsummary>Reset entry <c>I</c> to the default value for the array.
      </fsummary>
      <desc><marker id="reset-2"/>
        <p>Resets 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 is returned unchanged. Reset never changes the array
          size. Shrinking can be done explicitly by calling
          <seealso marker="#resize-2"><c>resize/2</c></seealso>.</p> 
        <p>If <c><anno>I</anno></c> is not a non-negative 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>; compare
          <seealso marker="#set-3"><c>set/3</c></seealso></p>
        <p>See also <seealso marker="#new-2"><c>new/2</c></seealso>,
          <seealso marker="#set-3"><c>set/3</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="resize" arity="1"/>
      <fsummary>Change the array size to that reported by <c>sparse_size/1</c>.
      </fsummary>
      <desc><marker id="resize-1"/>
        <p>Changes the array size to that reported by
          <seealso marker="#sparse_size-1"><c>sparse_size/1</c></seealso>. If
          the specified array has fixed size, also the resulting array has fixed
          size.</p>
        <p>See also <seealso marker="#resize-2"><c>resize/2</c></seealso>,
          <seealso marker="#sparse_size-1"><c>sparse_size/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="resize" arity="2"/>
      <fsummary>Change the array size.</fsummary>
      <desc><marker id="resize-2"/>
        <p>Change the array size. If <c><anno>Size</anno></c> is not a
          non-negative integer, the call fails with reason <c>badarg</c>. If
          the specified array has fixed size, also the resulting array has fixed
          size.</p>
      </desc>
    </func>

    <func>
      <name name="set" arity="3"/>
      <fsummary>Set entry <c>I</c> of the array to <c>Value</c>.</fsummary>
      <desc><marker id="set-3"/>
        <p>Sets entry <c><anno>I</anno></c> of the array to
          <c><anno>Value</anno></c>. If <c><anno>I</anno></c> is not a
          non-negative 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 grows to
          size <c><anno>I</anno>+1</c>.</p>
        <p>See also <seealso marker="#get-2"><c>get/2</c></seealso>,
          <seealso marker="#reset-2"><c>reset/2</c></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>Gets the number of entries in the array. Entries are numbered from
          <c>0</c> 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>See also <seealso marker="#set-3"><c>set/3</c></seealso>,
          <seealso marker="#sparse_size-1"><c>sparse_size/1</c></seealso>.</p>
      </desc>
    </func>

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

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

    <func>
      <name name="sparse_map" arity="2"/>
      <fsummary>Map the specified function onto each array element, skipping
        default-valued entries.</fsummary>
      <desc><marker id="sparse_map-2"/>
        <p>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 <c><anno>Function</anno></c> is not a
          function, the call fails with reason <c>badarg</c>.</p>
        <p>See also <seealso marker="#map-2"><c>map/2</c></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>Gets the number of entries in the array up until the last
          non-default-valued entry. That is, 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>See also <seealso marker="#resize-1"><c>resize/1</c></seealso>,
          <seealso marker="#size-1"><c>size/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="sparse_to_list" arity="1"/>
      <fsummary>Convert 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>See also <seealso marker="#to_list-1"><c>to_list/1</c></seealso>.</p>
      </desc>
    </func>

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

    <func>
      <name name="to_list" arity="1"/>
      <fsummary>Convert the array to a list.</fsummary>
      <desc><marker id="to_list-1"/>
        <p>Converts the array to a list.</p>
        <p>See also <seealso marker="#from_list-2"><c>from_list/2</c></seealso>,
          <seealso marker="#sparse_to_list-1"><c>sparse_to_list/1</c></seealso>.
        </p>
      </desc>
    </func>

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