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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>’.
</p>
<p>When called with a single argument, return a square matrix with the dimension
specified.
</p>
<p>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.
</p>
<p>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.
</p>
<p>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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