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<a name="Introduction-to-descriptive"></a>
<div class="header">
<p>
Next: <a href="maxima_207.html#Functions-and-Variables-for-data-manipulation" accesskey="n" rel="next">Functions and Variables for data manipulation</a>, Previous: <a href="maxima_205.html#descriptive_002dpkg" accesskey="p" rel="previous">descriptive-pkg</a>, Up: <a href="maxima_205.html#descriptive_002dpkg" accesskey="u" rel="up">descriptive-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_368.html#Function-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Introduction-to-descriptive-1"></a>
<h3 class="section">50.1 Introduction to descriptive</h3>
<p>Package <code>descriptive</code> contains a set of functions for
making descriptive statistical computations and graphing.
Together with the source code there are three data sets in
your Maxima tree: <code>pidigits.data</code>, <code>wind.data</code> and <code>biomed.data</code>.
</p>
<p>Any statistics manual can be used as a reference to the functions in package <code>descriptive</code>.
</p>
<p>For comments, bugs or suggestions, please contact me at <var>’riotorto AT yahoo DOT com’</var>.
</p>
<p>Here is a simple example on how the descriptive functions in <code>descriptive</code> do they work, depending on the nature of their arguments, lists or matrices,
</p>
<div class="example">
<pre class="example">(%i1) load ("descriptive")$
</pre><pre class="example">(%i2) /* univariate sample */ mean ([a, b, c]);
c + b + a
(%o2) ---------
3
</pre><pre class="example">(%i3) matrix ([a, b], [c, d], [e, f]);
[ a b ]
[ ]
(%o3) [ c d ]
[ ]
[ e f ]
</pre><pre class="example">(%i4) /* multivariate sample */ mean (%);
e + c + a f + d + b
(%o4) [---------, ---------]
3 3
</pre></div>
<p>Note that in multivariate samples the mean is calculated for each column.
</p>
<p>In case of several samples with possible different sizes, the Maxima function <code>map</code> can be used to get the desired results for each sample,
</p>
<div class="example">
<pre class="example">(%i1) load ("descriptive")$
</pre><pre class="example">(%i2) map (mean, [[a, b, c], [d, e]]);
c + b + a e + d
(%o2) [---------, -----]
3 2
</pre></div>
<p>In this case, two samples of sizes 3 and 2 were stored into a list.
</p>
<p>Univariate samples must be stored in lists like
</p>
<div class="example">
<pre class="example">(%i1) s1 : [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5];
(%o1) [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]
</pre></div>
<p>and multivariate samples in matrices as in
</p>
<div class="example">
<pre class="example">(%i1) s2 : matrix ([13.17, 9.29], [14.71, 16.88], [18.50, 16.88],
[10.58, 6.63], [13.33, 13.25], [13.21, 8.12]);
[ 13.17 9.29 ]
[ ]
[ 14.71 16.88 ]
[ ]
[ 18.5 16.88 ]
(%o1) [ ]
[ 10.58 6.63 ]
[ ]
[ 13.33 13.25 ]
[ ]
[ 13.21 8.12 ]
</pre></div>
<p>In this case, the number of columns equals the random variable dimension and the number of rows is the sample size.
</p>
<p>Data can be introduced by hand, but big samples are usually stored in plain text files. For example, file <code>pidigits.data</code> contains the first 100 digits of number <code>%pi</code>:
</p><div class="example">
<pre class="example"> 3
1
4
1
5
9
2
6
5
3 ...
</pre></div>
<p>In order to load these digits in Maxima,
</p>
<div class="example">
<pre class="example">(%i1) s1 : read_list (file_search ("pidigits.data"))$
</pre><pre class="example">(%i2) length (s1);
(%o2) 100
</pre></div>
<p>On the other hand, file <code>wind.data</code> contains daily average wind speeds at 5 meteorological stations in the Republic of Ireland (This is part of a data set taken at 12 meteorological stations. The original file is freely downloadable from the StatLib Data Repository and its analysis is discussed in Haslett, J., Raftery, A. E. (1989) <var>Space-time Modelling with Long-memory Dependence: Assessing Ireland’s Wind Power Resource, with Discussion</var>. Applied Statistics 38, 1-50). This loads the data:
</p>
<div class="example">
<pre class="example">(%i1) s2 : read_matrix (file_search ("wind.data"))$
</pre><pre class="example">(%i2) length (s2);
(%o2) 100
</pre><pre class="example">(%i3) s2 [%]; /* last record */
(%o3) [3.58, 6.0, 4.58, 7.62, 11.25]
</pre></div>
<p>Some samples contain non numeric data. As an example, file <code>biomed.data</code> (which is part of another bigger one downloaded from the StatLib Data Repository) contains four blood measures taken from two groups of patients, <code>A</code> and <code>B</code>, of different ages,
</p>
<div class="example">
<pre class="example">(%i1) s3 : read_matrix (file_search ("biomed.data"))$
</pre><pre class="example">(%i2) length (s3);
(%o2) 100
</pre><pre class="example">(%i3) s3 [1]; /* first record */
(%o3) [A, 30, 167.0, 89.0, 25.6, 364]
</pre></div>
<p>The first individual belongs to group <code>A</code>, is 30 years old and his/her blood measures were 167.0, 89.0, 25.6 and 364.
</p>
<p>One must take care when working with categorical data. In the next example, symbol <code>a</code> is assigned a value in some previous moment and then a sample with categorical value <code>a</code> is taken,
</p>
<div class="example">
<pre class="example">(%i1) a : 1$
</pre><pre class="example">(%i2) matrix ([a, 3], [b, 5]);
[ 1 3 ]
(%o2) [ ]
[ b 5 ]
</pre></div>
<div class=categorybox>·<p>Categories: <a href="maxima_369.html#Category_003a-Descriptive-statistics">Descriptive statistics</a>
·<a href="maxima_369.html#Category_003a-Share-packages">Share packages</a>
·<a href="maxima_369.html#Category_003a-Package-descriptive">Package descriptive</a>
</div></p>
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Next: <a href="maxima_207.html#Functions-and-Variables-for-data-manipulation" accesskey="n" rel="next">Functions and Variables for data manipulation</a>, Previous: <a href="maxima_205.html#descriptive_002dpkg" accesskey="p" rel="previous">descriptive-pkg</a>, Up: <a href="maxima_205.html#descriptive_002dpkg" accesskey="u" rel="up">descriptive-pkg</a> [<a href="maxima_toc.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="maxima_368.html#Function-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
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