# Perl Data Analytics Tutorial

## Let's find the standard deviation

I will explain how to find the standard deviation using a Perl program.

### Find the standard deviation

Consider the following array.

```my @array = (10, 50, 60, 65, 70, 90);
```

#### Sample program to find the standard deviation of an array

Actually find the standard deviation from the array. The Statistics::Lite module has a stddev function, but I won't use it in this example.

I will not explain how to calculate the standard deviation.

```use strict;
use warnings;

sub get_stddev {
return sqrt(get_disp(@_));
}

sub get_disp {
my (\$array_ref) = @_;
my \$mean = get_avg(\$array_ref);
my \$count = @\$array_ref;
my \$sum = 0;

for my \$num (@\$array_ref) {
\$sum += ((\$num - \$mean) ** 2);
}
return \$sum / \$count;
}

sub get_avg {
my (\$array_ref) = @_;
my \$count = @\$array_ref;
my \$sum = 0;
for my \$num (@\$array_ref) {
\$sum += \$num;
}
return \$sum / \$count;
}

my @array = (10, 50, 60, 65, 70, 90);
my \$stddev = get_stddev(\@array);
print "Standard deviation is " . \$stddev . "\n";
```

Execution result

```The standard deviation is 24.452334585202.
```

You can copy and paste this program and try it immediately at PerlBanjo.