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<a name="Missing-Data"></a>
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<a name="Missing-Data-1"></a>
<h4 class="subsection">3.1.2 Missing Data</h4>
<a name="index-missing-data"></a>
<p>It is possible to represent missing data explicitly in Octave using
<code>NA</code> (short for “Not Available”). Missing data can only be
represented when data is represented as floating point numbers. In this
case missing data is represented as a special case of the representation
of <code>NaN</code>.
</p>
<a name="XREFNA"></a><dl>
<dt><a name="index-NA"></a>Built-in Function: <em></em> <strong>NA</strong></dt>
<dt><a name="index-NA-1"></a>Built-in Function: <em></em> <strong>NA</strong> <em>(<var>n</var>)</em></dt>
<dt><a name="index-NA-2"></a>Built-in Function: <em></em> <strong>NA</strong> <em>(<var>n</var>, <var>m</var>)</em></dt>
<dt><a name="index-NA-3"></a>Built-in Function: <em></em> <strong>NA</strong> <em>(<var>n</var>, <var>m</var>, <var>k</var>, …)</em></dt>
<dt><a name="index-NA-4"></a>Built-in Function: <em></em> <strong>NA</strong> <em>(…, <var>class</var>)</em></dt>
<dd><p>Return a scalar, matrix, or N-dimensional array whose elements are all equal
to the special constant used to designate missing values.
</p>
<p>Note that NA always compares not equal to NA (NA != NA).
To find NA values, use the <code>isna</code> function.
</p>
<p>When called with no arguments, return a scalar with the value ‘<samp>NA</samp>’.
When called with a single argument, return a square matrix with the dimension
specified. When called with more than one scalar argument the first two
arguments are taken as the number of rows and columns and any further
arguments specify additional matrix dimensions.
The optional argument <var>class</var> specifies the return type and may be
either <code>"double"</code> or <code>"single"</code>.
</p>
<p><strong>See also:</strong> <a href="#XREFisna">isna</a>.
</p></dd></dl>
<a name="XREFisna"></a><dl>
<dt><a name="index-isna"></a>Mapping Function: <em></em> <strong>isna</strong> <em>(<var>x</var>)</em></dt>
<dd><p>Return a logical array which is true where the elements of <var>x</var> are
NA (missing) values and false where they are not.
For example:
</p>
<div class="example">
<pre class="example">isna ([13, Inf, NA, NaN])
⇒ [ 0, 0, 1, 0 ]
</pre></div>
<p><strong>See also:</strong> <a href="Finding-Elements-and-Checking-Conditions.html#XREFisnan">isnan</a>, <a href="Finding-Elements-and-Checking-Conditions.html#XREFisinf">isinf</a>, <a href="Finding-Elements-and-Checking-Conditions.html#XREFisfinite">isfinite</a>.
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