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<a name="Sets-1"></a>
<h2 class="chapter">27 Sets</h2>
<p>Octave has a number of functions for managing sets of data. A set is defined
as a collection of unique elements and is typically represented by a vector of
numbers sorted in ascending order. Any vector or matrix can be converted to a
set by removing duplicates through the use of the <code>unique</code> function.
However, it isn’t necessary to explicitly create a set as all of the functions
which operate on sets will convert their input to a set before proceeding.
</p>
<a name="XREFunique"></a><dl>
<dt><a name="index-unique"></a><em></em> <strong>unique</strong> <em>(<var>x</var>)</em></dt>
<dt><a name="index-unique-1"></a><em></em> <strong>unique</strong> <em>(<var>x</var>, "rows")</em></dt>
<dt><a name="index-unique-2"></a><em>[<var>y</var>, <var>i</var>, <var>j</var>] =</em> <strong>unique</strong> <em>(…)</em></dt>
<dt><a name="index-unique-3"></a><em>[<var>y</var>, <var>i</var>, <var>j</var>] =</em> <strong>unique</strong> <em>(…, "first")</em></dt>
<dt><a name="index-unique-4"></a><em>[<var>y</var>, <var>i</var>, <var>j</var>] =</em> <strong>unique</strong> <em>(…, "last")</em></dt>
<dd><p>Return the unique elements of <var>x</var> sorted in ascending order.
</p>
<p>If the input <var>x</var> is a column vector then return a column vector;
Otherwise, return a row vector. <var>x</var> may also be a cell array of
strings.
</p>
<p>If the optional argument <code>"rows"</code> is given then return the unique
rows of <var>x</var> sorted in ascending order. The input must be a 2-D matrix
to use this option.
</p>
<p>If requested, return index vectors <var>i</var> and <var>j</var> such that
<code><var>y</var> = <var>x</var>(<var>i</var>)</code> and <code><var>x</var> = <var>y</var>(<var>j</var>)</code>.
</p>
<p>Additionally, if <var>i</var> is a requested output then one of
<code>"first"</code> or <code>"last"</code> may be given as an input. If
<code>"last"</code> is specified, return the highest possible indices in
<var>i</var>, otherwise, if <code>"first"</code> is specified, return the lowest.
The default is <code>"last"</code>.
</p>
<p><strong>See also:</strong> <a href="Set-Operations.html#XREFunion">union</a>, <a href="Set-Operations.html#XREFintersect">intersect</a>, <a href="Set-Operations.html#XREFsetdiff">setdiff</a>, <a href="Set-Operations.html#XREFsetxor">setxor</a>, <a href="Set-Operations.html#XREFismember">ismember</a>.
</p></dd></dl>
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