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<a name="Object-Sizes"></a>
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<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>.
For any array, the result will always be larger 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>.
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 numerical. 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>.
</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 objects, the length is the number of rows or
columns, whichever is greater (this odd definition is used for compatibility
with <small>MATLAB</small>).
</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). Otherwise, return false.
</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. 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.
Trailing singleton dimensions are ignored.
Called with a single or no argument, size_equal 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.
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>
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