# Standard Deviation – Perl Script

When you need to be more accurate than average, you need standard deviation bro…

#!/usr/bin/perl

use strict;
print standard_deviation(1,2,3,4,5,6,7,8,9,10)."\n";

sub standard_deviation {

my(@numbers) = @_;

#Prevent division by 0 error in case you get junk data

return undef unless(scalar(@numbers));

# Step 1, find the mean of the numbers

my $total1 = 0;

foreach my $num (@numbers) {

$total1 += $num;

}

my $mean1 = $total1 / (scalar @numbers);

# Step 2, find the mean of the squares of the differences

# between each number and the mean

my $total2 = 0;

foreach my $num (@numbers) {

$total2 += ($mean1-$num)**2;

}

my $mean2 = $total2 / (scalar @numbers);

`# Step 3, standard deviation is the square root of the`

# above mean

my $std_dev = sqrt($mean2);

return $std_dev;

}

Here’s a rewrite of your standard deviation script in ruby if any of your visitors would be into that sort of thing:

#!/usr/bin/env ruby

#

def standard_deviation(*numbers)

return if numbers.size == 0

count = numbers.size

sum = numbers.reduce(&:+).to_f

mean = sum / count

sum_of_squares = numbers.reduce(0) { |r, n|

r + ((n – mean).abs ** 2)

}

variance = sum_of_squares / count

Math.sqrt(variance)

end

puts standard_deviation(1,2,3,4,5,6,7,8,9,10)

Nice!!

And here is the same program implemented in Haskell:

stdDev :: Floating a => [a] -> a

–What we get if we have an empty list

stdDev [] = 0

–Take square root of the Variance

stdDev xs = sqrt $ (sum $ map (^2) xs) / l – (sum xs / l) ^ 2

where l = fromIntegral $ length xs