### 21.10 Examples

Here is a basic example of how to use the statistical functions:

    #include <stdio.h>
    #include <gsl/gsl_statistics.h>

    int
    main(void)
    {
      double data[5] = {17.2, 18.1, 16.5, 18.3, 12.6};
      double mean, variance, largest, smallest;

      mean     = gsl_stats_mean(data, 1, 5);
      variance = gsl_stats_variance(data, 1, 5);
      largest  = gsl_stats_max(data, 1, 5);
      smallest = gsl_stats_min(data, 1, 5);

      printf ("The dataset is %g, %g, %g, %g, %g\n",
             data[0], data[1], data[2], data[3], data[4]);

      printf ("The sample mean is %g\n", mean);
      printf ("The estimated variance is %g\n", variance);
      printf ("The largest value is %g\n", largest);
      printf ("The smallest value is %g\n", smallest);
      return 0;
    }

The program should produce the following output,

    The dataset is 17.2, 18.1, 16.5, 18.3, 12.6
    The sample mean is 16.54
    The estimated variance is 5.373
    The largest value is 18.3
    The smallest value is 12.6

Here is an example using sorted data,

    #include <stdio.h>
    #include <gsl/gsl_sort.h>
    #include <gsl/gsl_statistics.h>

    int
    main(void)
    {
      double data[5] = {17.2, 18.1, 16.5, 18.3, 12.6};
      double median, upperq, lowerq;

      printf ("Original dataset:  %g, %g, %g, %g, %g\n",
             data[0], data[1], data[2], data[3], data[4]);

      gsl_sort (data, 1, 5);

      printf ("Sorted dataset: %g, %g, %g, %g, %g\n",
             data[0], data[1], data[2], data[3], data[4]);

      median
        = gsl_stats_median_from_sorted_data (data,
                                             1, 5);

      upperq
        = gsl_stats_quantile_from_sorted_data (data,
                                               1, 5,
                                               0.75);
      lowerq
        = gsl_stats_quantile_from_sorted_data (data,
                                               1, 5,
                                               0.25);

      printf ("The median is %g\n", median);
      printf ("The upper quartile is %g\n", upperq);
      printf ("The lower quartile is %g\n", lowerq);
      return 0;
    }

This program should produce the following output,

    Original dataset:  17.2, 18.1, 16.5, 18.3, 12.6
    Sorted dataset: 12.6, 16.5, 17.2, 18.1, 18.3
    The median is 17.2
    The upper quartile is 18.1
    The lower quartile is 16.5