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<a name="Manipulating-Structures"></a>
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<hr>
<a name="Manipulating-Structures-1"></a>
<h4 class="subsection">6.1.4 Manipulating Structures</h4>

<p>Other functions that can manipulate the fields of a structure are given below.
</p>
<a name="XREFnumfields"></a><dl>
<dt><a name="index-numfields"></a>: <em></em> <strong>numfields</strong> <em>(<var>s</var>)</em></dt>
<dd><p>Return the number of fields of the structure <var>s</var>.
</p>
<p><strong>See also:</strong> <a href="#XREFfieldnames">fieldnames</a>.
</p></dd></dl>


<a name="XREFfieldnames"></a><dl>
<dt><a name="index-fieldnames"></a>: <em><var>names</var> =</em> <strong>fieldnames</strong> <em>(<var>struct</var>)</em></dt>
<dt><a name="index-fieldnames-1"></a>: <em><var>names</var> =</em> <strong>fieldnames</strong> <em>(<var>obj</var>)</em></dt>
<dt><a name="index-fieldnames-2"></a>: <em><var>names</var> =</em> <strong>fieldnames</strong> <em>(<var>javaobj</var>)</em></dt>
<dt><a name="index-fieldnames-3"></a>: <em><var>names</var> =</em> <strong>fieldnames</strong> <em>(&quot;<var>javaclassname</var>&quot;)</em></dt>
<dd><p>Return a cell array of strings with the names of the fields in the
specified input.
</p>
<p>When the input is a structure <var>struct</var>, the names are the elements of
the structure.
</p>
<p>When the input is an Octave object <var>obj</var>, the names are the public
properties of the object.
</p>
<p>When the input is a Java object <var>javaobj</var> or a string containing the
name of a Java class <var>javaclassname</var>, the names are the public fields
(data members) of the object or class.
</p>
<p><strong>See also:</strong> <a href="#XREFnumfields">numfields</a>, <a href="#XREFisfield">isfield</a>, <a href="#XREForderfields">orderfields</a>, <a href="Creating-Structures.html#XREFstruct">struct</a>, <a href="Creating-a-Class.html#XREFmethods">methods</a>.
</p></dd></dl>


<a name="XREFisfield"></a><dl>
<dt><a name="index-isfield"></a>: <em></em> <strong>isfield</strong> <em>(<var>x</var>, &quot;<var>name</var>&quot;)</em></dt>
<dt><a name="index-isfield-1"></a>: <em></em> <strong>isfield</strong> <em>(<var>x</var>, <var>name</var>)</em></dt>
<dd><p>Return true if the <var>x</var> is a structure and it includes an element named
<var>name</var>.
</p>
<p>If <var>name</var> is a cell array of strings then a logical array of equal
dimension is returned.
</p>
<p><strong>See also:</strong> <a href="#XREFfieldnames">fieldnames</a>.
</p></dd></dl>


<a name="XREFsetfield"></a><dl>
<dt><a name="index-setfield"></a>: <em><var>sout</var> =</em> <strong>setfield</strong> <em>(<var>s</var>, <var>field</var>, <var>val</var>)</em></dt>
<dt><a name="index-setfield-1"></a>: <em><var>sout</var> =</em> <strong>setfield</strong> <em>(<var>s</var>, <var>sidx1</var>, <var>field1</var>, <var>fidx1</var>, <var>sidx2</var>, <var>field2</var>, <var>fidx2</var>, &hellip;, <var>val</var>)</em></dt>
<dd>
<p>Return a <em>copy</em> of the structure <var>s</var> with the field member
<var>field</var> set to the value <var>val</var>.
</p>
<p>For example:
</p>
<div class="example">
<pre class="example"><var>s</var> = struct ();
<var>s</var> = setfield (<var>s</var>, &quot;foo bar&quot;, 42);
</pre></div>

<p>This is equivalent to
</p>
<div class="example">
<pre class="example"><var>s</var>.(&quot;foo bar&quot;) = 42;
</pre></div>

<p>Note that ordinary structure syntax <code><var>s</var>.foo bar = 42</code> cannot be
used here, as the field name is not a valid Octave identifier because of
the space character.  Using arbitrary strings for field names is
incompatible with <small>MATLAB</small>, and this usage will emit a warning if the
warning ID <code>Octave:language-extension</code> is enabled.
See <a href="Issuing-Warnings.html#XREFwarning_005fids">warning_ids</a>.
</p>
<p>With the second calling form, set a field of a structure array.  The
input <var>sidx</var> selects an element of the structure array, <var>field</var>
specifies the field name of the selected element, and <var>fidx</var> selects
which element of the field (in the case of an array or cell array).
The <var>sidx</var>, <var>field</var>, and <var>fidx</var> inputs can be repeated to
address nested structure array elements.  The structure array index and
field element index must be cell arrays while the field name must be a
string.
</p>
<p>For example:
</p>
<div class="example">
<pre class="example"><var>s</var> = struct (&quot;baz&quot;, 42);
setfield (<var>s</var>, {1}, &quot;foo&quot;, {1}, &quot;bar&quot;, 54)
&rArr;
  ans =
    scalar structure containing the fields:
      baz =  42
      foo =
        scalar structure containing the fields:
          bar =  54
</pre></div>

<p>The example begins with an ordinary scalar structure to which a nested
scalar structure is added.  In all cases, if the structure index <var>sidx</var>
is not specified it defaults to 1 (scalar structure).  Thus, the example
above could be written more concisely as
<code>setfield (<var>s</var>, &quot;foo&quot;, &quot;bar&quot;, 54)</code>
</p>
<p>Finally, an example with nested structure arrays:
</p>
<div class="example">
<pre class="example"><var>sa</var>.foo = 1;
<var>sa</var> = setfield (<var>sa</var>, {2}, &quot;bar&quot;, {3}, &quot;baz&quot;, {1, 4}, 5);
<var>sa</var>(2).bar(3)
&rArr;
  ans =
    scalar structure containing the fields:
      baz =  0   0   0   5
</pre></div>

<p>Here <var>sa</var> is a structure array whose field at elements 1 and 2 is in
turn another structure array whose third element is a simple scalar
structure.  The terminal scalar structure has a field which contains a
matrix value.
</p>
<p>Note that the same result as in the above example could be achieved by:
</p>
<div class="example">
<pre class="example"><var>sa</var>.foo = 1;
<var>sa</var>(2).bar(3).baz(1,4) = 5
</pre></div>

<p><strong>See also:</strong> <a href="#XREFgetfield">getfield</a>, <a href="#XREFrmfield">rmfield</a>, <a href="#XREForderfields">orderfields</a>, <a href="#XREFisfield">isfield</a>, <a href="#XREFfieldnames">fieldnames</a>, <a href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>


<a name="XREFgetfield"></a><dl>
<dt><a name="index-getfield"></a>: <em><var>val</var> =</em> <strong>getfield</strong> <em>(<var>s</var>, <var>field</var>)</em></dt>
<dt><a name="index-getfield-1"></a>: <em><var>val</var> =</em> <strong>getfield</strong> <em>(<var>s</var>, <var>sidx1</var>, <var>field1</var>, <var>fidx1</var>, &hellip;)</em></dt>
<dd><p>Get the value of the field named <var>field</var> from a structure or nested
structure <var>s</var>.
</p>
<p>If <var>s</var> is a structure array then <var>sidx</var> selects an element of the
structure array, <var>field</var> specifies the field name of the selected
element, and <var>fidx</var> selects which element of the field (in the case of
an array or cell array).  See <code>setfield</code> for a more complete
description of the syntax.
</p>

<p><strong>See also:</strong> <a href="#XREFsetfield">setfield</a>, <a href="#XREFrmfield">rmfield</a>, <a href="#XREForderfields">orderfields</a>, <a href="#XREFisfield">isfield</a>, <a href="#XREFfieldnames">fieldnames</a>, <a href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>


<a name="XREFrmfield"></a><dl>
<dt><a name="index-rmfield"></a>: <em><var>sout</var> =</em> <strong>rmfield</strong> <em>(<var>s</var>, &quot;<var>f</var>&quot;)</em></dt>
<dt><a name="index-rmfield-1"></a>: <em><var>sout</var> =</em> <strong>rmfield</strong> <em>(<var>s</var>, <var>f</var>)</em></dt>
<dd><p>Return a <em>copy</em> of the structure (array) <var>s</var> with the field <var>f</var>
removed.
</p>
<p>If <var>f</var> is a cell array of strings or a character array, remove each of
the named fields.
</p>
<p><strong>See also:</strong> <a href="#XREForderfields">orderfields</a>, <a href="#XREFfieldnames">fieldnames</a>, <a href="#XREFisfield">isfield</a>.
</p></dd></dl>


<a name="XREForderfields"></a><dl>
<dt><a name="index-orderfields"></a>: <em><var>sout</var> =</em> <strong>orderfields</strong> <em>(<var>s1</var>)</em></dt>
<dt><a name="index-orderfields-1"></a>: <em><var>sout</var> =</em> <strong>orderfields</strong> <em>(<var>s1</var>, <var>s2</var>)</em></dt>
<dt><a name="index-orderfields-2"></a>: <em><var>sout</var> =</em> <strong>orderfields</strong> <em>(<var>s1</var>, {<var>cellstr</var>})</em></dt>
<dt><a name="index-orderfields-3"></a>: <em><var>sout</var> =</em> <strong>orderfields</strong> <em>(<var>s1</var>, <var>p</var>)</em></dt>
<dt><a name="index-orderfields-4"></a>: <em>[<var>sout</var>, <var>p</var>] =</em> <strong>orderfields</strong> <em>(&hellip;)</em></dt>
<dd><p>Return a <em>copy</em> of <var>s1</var> with fields arranged alphabetically, or as
specified by the second input.
</p>
<p>Given one input struct <var>s1</var>, arrange field names alphabetically.
</p>
<p>If a second struct argument is given, arrange field names in <var>s1</var> as
they appear in <var>s2</var>.  The second argument may also specify the order
in a cell array of strings <var>cellstr</var>.  The second argument may also
be a permutation vector.
</p>
<p>The optional second output argument <var>p</var> is the permutation vector which
converts the original name order to the new name order.
</p>
<p>Examples:
</p>
<div class="example">
<pre class="example">s = struct (&quot;d&quot;, 4, &quot;b&quot;, 2, &quot;a&quot;, 1, &quot;c&quot;, 3);
t1 = orderfields (s)
     &rArr; t1 =
        {
          a =  1
          b =  2
          c =  3
          d =  4
        }
</pre></div>

<div class="example">
<pre class="example">t = struct (&quot;d&quot;, {}, &quot;c&quot;, {}, &quot;b&quot;, {}, &quot;a&quot;, {});
t2 = orderfields (s, t)
     &rArr; t2 =
        {
          d =  4
          c =  3
          b =  2
          a =  1
        }
</pre></div>

<div class="example">
<pre class="example">t3 = orderfields (s, [3, 2, 4, 1])
     &rArr; t3 =
        {
          a =  1
          b =  2
          c =  3
          d =  4
        }
</pre></div>

<div class="example">
<pre class="example">[t4, p] = orderfields (s, {&quot;d&quot;, &quot;c&quot;, &quot;b&quot;, &quot;a&quot;})
     &rArr; t4 =
        {
          d =  4
          c =  3
          b =  2
          a =  1
        }
        p =
           1
           4
           2
           3
</pre></div>


<p><strong>See also:</strong> <a href="#XREFfieldnames">fieldnames</a>, <a href="#XREFgetfield">getfield</a>, <a href="#XREFsetfield">setfield</a>, <a href="#XREFrmfield">rmfield</a>, <a href="#XREFisfield">isfield</a>, <a href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>


<a name="XREFsubstruct"></a><dl>
<dt><a name="index-substruct"></a>: <em></em> <strong>substruct</strong> <em>(<var>type</var>, <var>subs</var>, &hellip;)</em></dt>
<dd><p>Create a subscript structure for use with <code>subsref</code> or <code>subsasgn</code>.
</p>
<p>For example:
</p>
<div class="example">
<pre class="example">idx = substruct (&quot;()&quot;, {3, &quot;:&quot;})
     &rArr;
       idx =
       {
         type = ()
         subs =
         {
           [1,1] =  3
           [1,2] = :
         }
       }
x = [1, 2, 3;
     4, 5, 6;
     7, 8, 9];
subsref (x, idx)
   &rArr; 7  8  9
</pre></div>

<p><strong>See also:</strong> <a href="Defining-Indexing-And-Indexed-Assignment.html#XREFsubsref">subsref</a>, <a href="Defining-Indexing-And-Indexed-Assignment.html#XREFsubsasgn">subsasgn</a>.
</p></dd></dl>


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