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<h4 class="subsection" id="Manipulating-Structures-1"><span>6.1.4 Manipulating Structures<a class="copiable-link" href="#Manipulating-Structures-1"> ¶</a></span></h4>
<p>Other functions that can manipulate the fields of a structure are given below.
</p>
<a class="anchor" id="XREFnumfields"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-numfields"><span><code class="def-type"><var class="var">n</var> =</code> <strong class="def-name">numfields</strong> <code class="def-code-arguments">(<var class="var">s</var>)</code><a class="copiable-link" href="#index-numfields"> ¶</a></span></dt>
<dd><p>Return the number of fields of the structure <var class="var">s</var>.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfieldnames">fieldnames</a>.
</p></dd></dl>
<a class="anchor" id="XREFfieldnames"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-fieldnames"><span><code class="def-type"><var class="var">names</var> =</code> <strong class="def-name">fieldnames</strong> <code class="def-code-arguments">(<var class="var">struct</var>)</code><a class="copiable-link" href="#index-fieldnames"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-fieldnames-1"><span><code class="def-type"><var class="var">names</var> =</code> <strong class="def-name">fieldnames</strong> <code class="def-code-arguments">(<var class="var">obj</var>)</code><a class="copiable-link" href="#index-fieldnames-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-fieldnames-2"><span><code class="def-type"><var class="var">names</var> =</code> <strong class="def-name">fieldnames</strong> <code class="def-code-arguments">(<var class="var">javaobj</var>)</code><a class="copiable-link" href="#index-fieldnames-2"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-fieldnames-3"><span><code class="def-type"><var class="var">names</var> =</code> <strong class="def-name">fieldnames</strong> <code class="def-code-arguments">("<var class="var">javaclassname</var>")</code><a class="copiable-link" href="#index-fieldnames-3"> ¶</a></span></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 class="var">struct</var>, the <var class="var">names</var> are the elements
of the structure.
</p>
<p>When the input is an Octave object <var class="var">obj</var>, the <var class="var">names</var> are the public
properties of the object.
</p>
<p>When the input is a Java object <var class="var">javaobj</var> or a string containing the
name of a Java class <var class="var">javaclassname</var>, the <var class="var">names</var> are the public
fields (data members) of the object or class.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFnumfields">numfields</a>, <a class="ref" href="#XREFisfield">isfield</a>, <a class="ref" href="#XREForderfields">orderfields</a>, <a class="ref" href="Creating-Structures.html#XREFstruct">struct</a>, <a class="ref" href="Properties.html#XREFproperties">properties</a>.
</p></dd></dl>
<a class="anchor" id="XREFisfield"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-isfield"><span><code class="def-type"><var class="var">tf</var> =</code> <strong class="def-name">isfield</strong> <code class="def-code-arguments">(<var class="var">x</var>, "<var class="var">name</var>")</code><a class="copiable-link" href="#index-isfield"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-isfield-1"><span><code class="def-type"><var class="var">tf</var> =</code> <strong class="def-name">isfield</strong> <code class="def-code-arguments">(<var class="var">x</var>, <var class="var">name</var>)</code><a class="copiable-link" href="#index-isfield-1"> ¶</a></span></dt>
<dd><p>Return true if the <var class="var">x</var> is a structure and it includes an element named
<var class="var">name</var>.
</p>
<p>If <var class="var">name</var> is a cell array of strings then a logical array of equal
dimension is returned.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfieldnames">fieldnames</a>.
</p></dd></dl>
<a class="anchor" id="XREFsetfield"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-setfield"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">setfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, <var class="var">field</var>, <var class="var">val</var>)</code><a class="copiable-link" href="#index-setfield"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-setfield-1"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">setfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, <var class="var">sidx1</var>, <var class="var">field1</var>, <var class="var">fidx1</var>, <var class="var">sidx2</var>, <var class="var">field2</var>, <var class="var">fidx2</var>, …, <var class="var">val</var>)</code><a class="copiable-link" href="#index-setfield-1"> ¶</a></span></dt>
<dd>
<p>Return a <em class="emph">copy</em> of the structure <var class="var">s</var> with the field member
<var class="var">field</var> set to the value <var class="var">val</var>.
</p>
<p>For example:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted"><var class="var">s</var> = struct ();
<var class="var">s</var> = setfield (<var class="var">s</var>, "foo bar", 42);
</pre></div></div>
<p>This is equivalent to
</p>
<div class="example">
<pre class="example-preformatted"><var class="var">s</var>.("foo bar") = 42;
</pre></div>
<p>Note that ordinary structure syntax <code class="code"><var class="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 class="sc">MATLAB</small>, and this usage will emit a warning if the
warning ID <code class="code">Octave:language-extension</code> is enabled.
See <a class="xref" href="Issuing-Warnings.html#XREFwarning_005fids"><code class="code">warning_ids</code></a>.
</p>
<p>With the second calling form, set a field of a structure array. The
input <var class="var">sidx</var> selects an element of the structure array, <var class="var">field</var>
specifies the field name of the selected element, and <var class="var">fidx</var> selects
which element of the field (in the case of an array or cell array).
The <var class="var">sidx</var>, <var class="var">field</var>, and <var class="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">
<div class="group"><pre class="example-preformatted"><var class="var">s</var> = struct ("baz", 42);
setfield (<var class="var">s</var>, {1}, "foo", {1}, "bar", 54)
⇒
ans =
scalar structure containing the fields:
baz = 42
foo =
scalar structure containing the fields:
bar = 54
</pre></div></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 class="var">sidx</var>
is not specified it defaults to 1 (scalar structure). Thus, the example
above could be written more concisely as
<code class="code">setfield (<var class="var">s</var>, "foo", "bar", 54)</code>
</p>
<p>Finally, an example with nested structure arrays:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted"><var class="var">sa</var>.foo = 1;
<var class="var">sa</var> = setfield (<var class="var">sa</var>, {2}, "bar", {3}, "baz", {1, 4}, 5);
<var class="var">sa</var>(2).bar(3)
⇒
ans =
scalar structure containing the fields:
baz = 0 0 0 5
</pre></div></div>
<p>Here <var class="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">
<div class="group"><pre class="example-preformatted"><var class="var">sa</var>.foo = 1;
<var class="var">sa</var>(2).bar(3).baz(1,4) = 5
</pre></div></div>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFgetfield">getfield</a>, <a class="ref" href="#XREFrmfield">rmfield</a>, <a class="ref" href="#XREForderfields">orderfields</a>, <a class="ref" href="#XREFisfield">isfield</a>, <a class="ref" href="#XREFfieldnames">fieldnames</a>, <a class="ref" href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a class="ref" href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>
<a class="anchor" id="XREFgetfield"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-getfield"><span><code class="def-type"><var class="var">val</var> =</code> <strong class="def-name">getfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, <var class="var">field</var>)</code><a class="copiable-link" href="#index-getfield"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-getfield-1"><span><code class="def-type"><var class="var">val</var> =</code> <strong class="def-name">getfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, <var class="var">sidx1</var>, <var class="var">field1</var>, <var class="var">fidx1</var>, …)</code><a class="copiable-link" href="#index-getfield-1"> ¶</a></span></dt>
<dd><p>Get the value of the field named <var class="var">field</var> from a structure or nested
structure <var class="var">s</var>.
</p>
<p>If <var class="var">s</var> is a structure array then <var class="var">sidx</var> selects an element of the
structure array, <var class="var">field</var> specifies the field name of the selected
element, and <var class="var">fidx</var> selects which element of the field (in the case of
an array or cell array). For a more complete description of the syntax,
see <a class="pxref" href="#XREFsetfield"><code class="code">setfield</code></a>.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFsetfield">setfield</a>, <a class="ref" href="#XREFrmfield">rmfield</a>, <a class="ref" href="#XREForderfields">orderfields</a>, <a class="ref" href="#XREFisfield">isfield</a>, <a class="ref" href="#XREFfieldnames">fieldnames</a>, <a class="ref" href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a class="ref" href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>
<a class="anchor" id="XREFrmfield"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-rmfield"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">rmfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, "<var class="var">f</var>")</code><a class="copiable-link" href="#index-rmfield"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-rmfield-1"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">rmfield</strong> <code class="def-code-arguments">(<var class="var">s</var>, <var class="var">f</var>)</code><a class="copiable-link" href="#index-rmfield-1"> ¶</a></span></dt>
<dd><p>Return a <em class="emph">copy</em> of the structure (array) <var class="var">s</var> with the field <var class="var">f</var>
removed.
</p>
<p>If <var class="var">f</var> is a cell array of strings or a character array, remove each of
the named fields.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREForderfields">orderfields</a>, <a class="ref" href="#XREFfieldnames">fieldnames</a>, <a class="ref" href="#XREFisfield">isfield</a>.
</p></dd></dl>
<a class="anchor" id="XREForderfields"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-orderfields"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">orderfields</strong> <code class="def-code-arguments">(<var class="var">s1</var>)</code><a class="copiable-link" href="#index-orderfields"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-orderfields-1"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">orderfields</strong> <code class="def-code-arguments">(<var class="var">s1</var>, <var class="var">s2</var>)</code><a class="copiable-link" href="#index-orderfields-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-orderfields-2"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">orderfields</strong> <code class="def-code-arguments">(<var class="var">s1</var>, {<var class="var">cellstr</var>})</code><a class="copiable-link" href="#index-orderfields-2"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-orderfields-3"><span><code class="def-type"><var class="var">sout</var> =</code> <strong class="def-name">orderfields</strong> <code class="def-code-arguments">(<var class="var">s1</var>, <var class="var">p</var>)</code><a class="copiable-link" href="#index-orderfields-3"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-orderfields-4"><span><code class="def-type">[<var class="var">sout</var>, <var class="var">p</var>] =</code> <strong class="def-name">orderfields</strong> <code class="def-code-arguments">(…)</code><a class="copiable-link" href="#index-orderfields-4"> ¶</a></span></dt>
<dd><p>Return a <em class="emph">copy</em> of <var class="var">s1</var> with fields arranged alphabetically, or as
specified by the second input.
</p>
<p>Given one input struct <var class="var">s1</var>, arrange field names alphabetically.
</p>
<p>If a second struct argument is given, arrange field names in <var class="var">s1</var> as
they appear in <var class="var">s2</var>. The second argument may also specify the order
in a cell array of strings <var class="var">cellstr</var>. The second argument may also
be a permutation vector.
</p>
<p>The optional second output argument <var class="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">
<div class="group"><pre class="example-preformatted">s = struct ("d", 4, "b", 2, "a", 1, "c", 3);
t1 = orderfields (s)
⇒ t1 =
scalar structure containing the fields:
a = 1
b = 2
c = 3
d = 4
</pre></div></div>
<div class="example">
<div class="group"><pre class="example-preformatted">t = struct ("d", {}, "c", {}, "b", {}, "a", {});
t2 = orderfields (s, t)
⇒ t2 =
scalar structure containing the fields:
d = 4
c = 3
b = 2
a = 1
</pre></div></div>
<div class="example">
<div class="group"><pre class="example-preformatted">t3 = orderfields (s, [3, 2, 4, 1])
⇒ t3 =
scalar structure containing the fields:
a = 1
b = 2
c = 3
d = 4
</pre></div></div>
<div class="example">
<div class="group"><pre class="example-preformatted">[t4, p] = orderfields (s, {"d", "c", "b", "a"})
⇒ t4 =
scalar structure containing the fields:
d = 4
c = 3
b = 2
a = 1
p =
1
4
2
3
</pre></div></div>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfieldnames">fieldnames</a>, <a class="ref" href="#XREFgetfield">getfield</a>, <a class="ref" href="#XREFsetfield">setfield</a>, <a class="ref" href="#XREFrmfield">rmfield</a>, <a class="ref" href="#XREFisfield">isfield</a>, <a class="ref" href="Creating-Structures.html#XREFisstruct">isstruct</a>, <a class="ref" href="Creating-Structures.html#XREFstruct">struct</a>.
</p></dd></dl>
<a class="anchor" id="XREFsubstruct"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-substruct"><span><code class="def-type"><var class="var">s</var> =</code> <strong class="def-name">substruct</strong> <code class="def-code-arguments">(<var class="var">type</var>, <var class="var">subs</var>, …)</code><a class="copiable-link" href="#index-substruct"> ¶</a></span></dt>
<dd><p>Create a subscript structure for use with <code class="code">subsref</code> or <code class="code">subsasgn</code>.
</p>
<p>For example:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">idx = substruct ("()", {3, ":"})
⇒ idx =
scalar structure containing the fields:
type = ()
subs =
{
[1,1] = 3
[1,2] = :
}
x = [1, 2, 3;
4, 5, 6;
7, 8, 9];
subsref (x, idx)
⇒ 7 8 9
</pre></div></div>
<p>Note: The keyword <code class="code">end</code> cannot be used within <code class="code">subsref</code> or
<code class="code">subsasgn</code> for indexing assignments.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="Defining-Indexing-And-Indexed-Assignment.html#XREFsubsref">subsref</a>, <a class="ref" href="Defining-Indexing-And-Indexed-Assignment.html#XREFsubsasgn">subsasgn</a>.
</p></dd></dl>
</div>
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