perl standard deviation

pond2539

　　perl自带的标准差模块确实难用，找了个这个：
　　http://andrewstechhints.blogspot.com/2010/02/standard-deviation-in-perl.html



#!/usr/bin/perl
use strict;
use warnings;
my @my_array = (1,6,9,2,5,12,1);
my $average = average(@my_array);
my $std_dev = std_dev($average, @my_array);
printf "avg=%.2f, st. dev=%.2f\n", $average, $std_dev;
sub average {
my (@values) = @_;
my $count = scalar @values;
my $total = 0;
$total += $_ for @values;
return $count ? $total / $count : 0;
}
sub std_dev {
my ($average, @values) = @_;
my $count = scalar @values;
my $std_dev_sum = 0;
$std_dev_sum += ($_ - $average) ** 2 for @values;
return $count ? sqrt($std_dev_sum / $count) : 0;
}