math_gsl_statistics_quantile

#!/usr/local/bin/perl
use strict;
use warnings;
use Math::GSL::Statistics qw/:all/;

# gsl113.pdf p315
# 20.9 中央値と百分位数
#
# gsl_stats_quantile_from_sorted_data($sorted_data, $stride, $n, $f)
#

=begin

  {

   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;

   }

   このプログラムは以下のように出力する。

   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
   20.11

=cut

my $correct = <<EOF
Correct

   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
   20.11

EOF
;

print $correct;

my $sorted_data = [ sort {$a <=> $b} qw/17.2 18.1 16.5 18.3 12.6/ ];

my $median = gsl_stats_median_from_sorted_data( $sorted_data, 1, scalar(@$sorted_data) );
my $upperq = gsl_stats_quantile_from_sorted_data( $sorted_data, 1, scalar(@$sorted_data) , 0.75);
my $lowerq = gsl_stats_quantile_from_sorted_data( $sorted_data, 1, scalar(@$sorted_data) , 0.25);

print "The median is ${median}\n";
print "The upper quantile is ${upperq}\n";
print "The lower quantile is ${lowerq}\n";