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<a name="Object-Sizes"></a>
<div class="header">
<p>
Previous: <a href="User_002ddefined-Data-Types.html#User_002ddefined-Data-Types" accesskey="p" rel="prev">User-defined Data Types</a>, Up: <a href="Data-Types.html#Data-Types" accesskey="u" rel="up">Data Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Object-Sizes-1"></a>
<h3 class="section">3.3 Object Sizes</h3>
<p>The following functions allow you to determine the size of a variable or
expression. These functions are defined for all objects. They return
-1 when the operation doesn’t make sense. For example, Octave’s
data structure type doesn’t have rows or columns, so the <code>rows</code> and
<code>columns</code> functions return -1 for structure arguments.
</p>
<a name="XREFndims"></a><dl>
<dt><a name="index-ndims"></a>Built-in Function: <em></em> <strong>ndims</strong> <em>(<var>a</var>)</em></dt>
<dd><p>Return the number of dimensions of <var>a</var>.
</p>
<p>For any array, the result will always be greater than or equal to 2.
Trailing singleton dimensions are not counted.
</p>
<div class="example">
<pre class="example">ndims (ones (4, 1, 2, 1))
⇒ 3
</pre></div>
<p><strong>See also:</strong> <a href="#XREFsize">size</a>.
</p></dd></dl>
<a name="XREFcolumns"></a><dl>
<dt><a name="index-columns"></a>Built-in Function: <em></em> <strong>columns</strong> <em>(<var>a</var>)</em></dt>
<dd><p>Return the number of columns of <var>a</var>.
</p>
<p><strong>See also:</strong> <a href="#XREFrows">rows</a>, <a href="#XREFsize">size</a>, <a href="#XREFlength">length</a>, <a href="#XREFnumel">numel</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisscalar">isscalar</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisvector">isvector</a>, <a href="Predicates-for-Numeric-Objects.html#XREFismatrix">ismatrix</a>.
</p></dd></dl>
<a name="XREFrows"></a><dl>
<dt><a name="index-rows"></a>Built-in Function: <em></em> <strong>rows</strong> <em>(<var>a</var>)</em></dt>
<dd><p>Return the number of rows of <var>a</var>.
</p>
<p><strong>See also:</strong> <a href="#XREFcolumns">columns</a>, <a href="#XREFsize">size</a>, <a href="#XREFlength">length</a>, <a href="#XREFnumel">numel</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisscalar">isscalar</a>, <a href="Predicates-for-Numeric-Objects.html#XREFisvector">isvector</a>, <a href="Predicates-for-Numeric-Objects.html#XREFismatrix">ismatrix</a>.
</p></dd></dl>
<a name="XREFnumel"></a><dl>
<dt><a name="index-numel"></a>Built-in Function: <em></em> <strong>numel</strong> <em>(<var>a</var>)</em></dt>
<dt><a name="index-numel-1"></a>Built-in Function: <em></em> <strong>numel</strong> <em>(<var>a</var>, <var>idx1</var>, <var>idx2</var>, …)</em></dt>
<dd><p>Return the number of elements in the object <var>a</var>.
</p>
<p>Optionally, if indices <var>idx1</var>, <var>idx2</var>, … are supplied,
return the number of elements that would result from the indexing
</p>
<div class="example">
<pre class="example"><var>a</var>(<var>idx1</var>, <var>idx2</var>, …)
</pre></div>
<p>Note that the indices do not have to be scalar numbers. For example,
</p>
<div class="example">
<pre class="example"><var>a</var> = 1;
<var>b</var> = ones (2, 3);
numel (<var>a</var>, <var>b</var>)
</pre></div>
<p>will return 6, as this is the number of ways to index with <var>b</var>.
Or the index could be the string <code>":"</code> which represents the colon
operator. For example,
</p>
<div class="example">
<pre class="example"><var>a</var> = ones (5, 3);
numel (<var>a</var>, 2, ":")
</pre></div>
<p>will return 3 as the second row has three column entries.
</p>
<p>This method is also called when an object appears as lvalue with cs-list
indexing, i.e., <code>object{…}</code> or <code>object(…).field</code>.
</p>
<p><strong>See also:</strong> <a href="#XREFsize">size</a>.
</p></dd></dl>
<a name="XREFlength"></a><dl>
<dt><a name="index-length"></a>Built-in Function: <em></em> <strong>length</strong> <em>(<var>a</var>)</em></dt>
<dd><p>Return the length of the object <var>a</var>.
</p>
<p>The length is 0 for empty objects, 1 for scalars, and the number of elements
for vectors. For matrix or N-dimensional objects, the length is the number
of elements along the largest dimension
(equivalent to <code>max (size (<var>a</var>))</code><!-- /@w -->).
</p>
<p><strong>See also:</strong> <a href="#XREFnumel">numel</a>, <a href="#XREFsize">size</a>.
</p></dd></dl>
<a name="XREFsize"></a><dl>
<dt><a name="index-size"></a>Built-in Function: <em></em> <strong>size</strong> <em>(<var>a</var>)</em></dt>
<dt><a name="index-size-1"></a>Built-in Function: <em></em> <strong>size</strong> <em>(<var>a</var>, <var>dim</var>)</em></dt>
<dd><p>Return the number of rows and columns of <var>a</var>.
</p>
<p>With one input argument and one output argument, the result is returned
in a row vector. If there are multiple output arguments, the number of
rows is assigned to the first, and the number of columns to the second,
etc. For example:
</p>
<div class="example">
<pre class="example">size ([1, 2; 3, 4; 5, 6])
⇒ [ 3, 2 ]
[nr, nc] = size ([1, 2; 3, 4; 5, 6])
⇒ nr = 3
⇒ nc = 2
</pre></div>
<p>If given a second argument, <code>size</code> will return the size of the
corresponding dimension. For example,
</p>
<div class="example">
<pre class="example">size ([1, 2; 3, 4; 5, 6], 2)
⇒ 2
</pre></div>
<p>returns the number of columns in the given matrix.
</p>
<p><strong>See also:</strong> <a href="#XREFnumel">numel</a>, <a href="#XREFndims">ndims</a>, <a href="#XREFlength">length</a>, <a href="#XREFrows">rows</a>, <a href="#XREFcolumns">columns</a>.
</p></dd></dl>
<a name="XREFisempty"></a><dl>
<dt><a name="index-isempty"></a>Built-in Function: <em></em> <strong>isempty</strong> <em>(<var>a</var>)</em></dt>
<dd><p>Return true if <var>a</var> is an empty matrix (any one of its dimensions is
zero).
</p>
<p><strong>See also:</strong> <a href="#XREFisnull">isnull</a>, <a href="Built_002din-Data-Types.html#XREFisa">isa</a>.
</p></dd></dl>
<a name="XREFisnull"></a><dl>
<dt><a name="index-isnull"></a>Built-in Function: <em></em> <strong>isnull</strong> <em>(<var>x</var>)</em></dt>
<dd><p>Return true if <var>x</var> is a special null matrix, string, or single quoted
string.
</p>
<p>Indexed assignment with such a value on the right-hand side should delete
array elements. This function should be used when overloading indexed
assignment for user-defined classes instead of <code>isempty</code>, to
distinguish the cases:
</p>
<dl compact="compact">
<dt><code>A(I) = []</code></dt>
<dd><p>This should delete elements if <code>I</code> is nonempty.
</p>
</dd>
<dt><code>X = []; A(I) = X</code></dt>
<dd><p>This should give an error if <code>I</code> is nonempty.
</p></dd>
</dl>
<p><strong>See also:</strong> <a href="#XREFisempty">isempty</a>, <a href="Advanced-Indexing.html#XREFisindex">isindex</a>.
</p></dd></dl>
<a name="XREFsizeof"></a><dl>
<dt><a name="index-sizeof"></a>Built-in Function: <em></em> <strong>sizeof</strong> <em>(<var>val</var>)</em></dt>
<dd><p>Return the size of <var>val</var> in bytes.
</p>
<p><strong>See also:</strong> <a href="Status-of-Variables.html#XREFwhos">whos</a>.
</p></dd></dl>
<a name="XREFsize_005fequal"></a><dl>
<dt><a name="index-size_005fequal"></a>Built-in Function: <em></em> <strong>size_equal</strong> <em>(<var>a</var>, <var>b</var>, …)</em></dt>
<dd><p>Return true if the dimensions of all arguments agree.
</p>
<p>Trailing singleton dimensions are ignored.
When called with a single or no argument <code>size_equal</code> returns true.
</p>
<p><strong>See also:</strong> <a href="#XREFsize">size</a>, <a href="#XREFnumel">numel</a>, <a href="#XREFndims">ndims</a>.
</p></dd></dl>
<a name="XREFsqueeze"></a><dl>
<dt><a name="index-squeeze"></a>Built-in Function: <em></em> <strong>squeeze</strong> <em>(<var>x</var>)</em></dt>
<dd><p>Remove singleton dimensions from <var>x</var> and return the result.
</p>
<p>Note that for compatibility with <small>MATLAB</small>, all objects have
a minimum of two dimensions and row vectors are left unchanged.
</p>
<p><strong>See also:</strong> <a href="Rearranging-Matrices.html#XREFreshape">reshape</a>.
</p></dd></dl>
<hr>
<div class="header">
<p>
Previous: <a href="User_002ddefined-Data-Types.html#User_002ddefined-Data-Types" accesskey="p" rel="prev">User-defined Data Types</a>, Up: <a href="Data-Types.html#Data-Types" accesskey="u" rel="up">Data Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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