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<a name="Example-programs-for-histograms"></a>
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<p>
Next: <a href="Two-dimensional-histograms.html#Two-dimensional-histograms" accesskey="n" rel="next">Two dimensional histograms</a>, Previous: <a href="The-histogram-probability-distribution-struct.html#The-histogram-probability-distribution-struct" accesskey="p" rel="previous">The histogram probability distribution struct</a>, Up: <a href="Histograms.html#Histograms" accesskey="u" rel="up">Histograms</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Example-programs-for-histograms-1"></a>
<h3 class="section">22.11 Example programs for histograms</h3>
<p>The following program shows how to make a simple histogram of a column
of numerical data supplied on <code>stdin</code>. The program takes three
arguments, specifying the upper and lower bounds of the histogram and
the number of bins. It then reads numbers from <code>stdin</code>, one line at
a time, and adds them to the histogram. When there is no more data to
read it prints out the accumulated histogram using
<code>gsl_histogram_fprintf</code>.
</p>
<div class="example">
<pre class="verbatim">#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_histogram.h>
int
main (int argc, char **argv)
{
double a, b;
size_t n;
if (argc != 4)
{
printf ("Usage: gsl-histogram xmin xmax n\n"
"Computes a histogram of the data "
"on stdin using n bins from xmin "
"to xmax\n");
exit (0);
}
a = atof (argv[1]);
b = atof (argv[2]);
n = atoi (argv[3]);
{
double x;
gsl_histogram * h = gsl_histogram_alloc (n);
gsl_histogram_set_ranges_uniform (h, a, b);
while (fscanf (stdin, "%lg", &x) == 1)
{
gsl_histogram_increment (h, x);
}
gsl_histogram_fprintf (stdout, h, "%g", "%g");
gsl_histogram_free (h);
}
exit (0);
}
</pre></div>
<p>Here is an example of the program in use. We generate 10000 random
samples from a Cauchy distribution with a width of 30 and histogram
them over the range -100 to 100, using 200 bins.
</p>
<div class="example">
<pre class="example">$ gsl-randist 0 10000 cauchy 30
| gsl-histogram -100 100 200 > histogram.dat
</pre></div>
<p>A plot of the resulting histogram shows the familiar shape of the
Cauchy distribution and the fluctuations caused by the finite sample
size.
</p>
<div class="example">
<pre class="example">$ awk '{print $1, $3 ; print $2, $3}' histogram.dat
| graph -T X
</pre></div>
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