It is just boiler-plate code (that you may simply have copied).

Are you claiming you know how to read a file into an array but not how to loop in Perl?

Your problem is to parse the data then partition the data and compute mean and std dev on the paritions.

Before I provide any more feedback I would like to see an attempt there as otherwise I have the feeling you are simply trying to free-ride.

This site is the Perl-monks, not the homework-monks.

so this is were l am stuck, once l have the data into the @data array i am not sure how to work through this to to the stats calculation by matching the col1 and col2 ranges.

#!/usr/bin/perl -w
# -------------------------------------------------
use strict;
use Getopt::Long;
use Pod::Usage;
use File::Spec;
Getopt::Long::Configure ("bundling");
use Statistics::R;
# -------------------------------------------------
my $help = 0;
my $force = 0;
my $verbose = 0;
my $result = GetOptions(
    "help|h" =>\$help,
    "force|f"=>\$force, 
    "verbose|v"=>\$verbose,
    );
#--------------------------------------------------
# Assign input data to an arrray
#---------------------------------------------------
scalar (@ARGV) == 1 or die pod2usage(1);
my $fname = $ARGV[0];
my $fnameout = $fname;
$fnameout =~ s/\.\w\w\w$/_conv.csv/;
# -------------------------------------------------
(-e $fname) or die "Unable to find input file: $fname\n";
(-e $fnameout and $force) and die "Output file already exisys. Use -f 
+to force: $fnameout\n";
my ($fin, $fout);
open ($fin, "<$fname") or die "Unable to open file: $fname\n";
open ($fout, ">$fnameout") or die "Unable to open output file: $fnameo
+ut\n";
my @headers = qw (Col_1 Col_3 Mean St_Dev);
print $fout (join (",", @headers),"\n");
# -------------------------------------------------
# Chomp all data
# -------------------------------------------------
my $cnt = 0;
my @data=();
my $line;
while (defined($line=<$fin>))
{
    $cnt ++;
    next unless $cnt > 1;                # Skip Header
    chomp($line);
    next if $line =~ /^\s*$/;
    my @cols = split(',',$line);
         push @data,[@cols];
}
[download]

You need to partition the data - that is you need to process the subsets given by "Col 1" and "Col 3" (i.e. name and id).

So one way of doing this would be to use a hash that uses an array-ref to collect the data belonging to one partition:

  my %partitions;
  while (
  ...
  my @cols = split(',', $line);
  my $pname = "$cols[0]:$cols[2]";
  $partitions{$pname} ||= [];
  push @{$partitions{$pname}}, $cols[3];
  }
[download]

Then you can later process these partitions to calculate e.g. the mean:

  use List::Util qw(sum);

  for my $pname (sort keys %partitions) {

     my $count = scalar @{$partition{$pname}};
     my $sum = sum @{$partition{$pname}};
     my $mean = $sum/$count;
     
     # std dev is left as an exercise
  }
[download]

This assumes that the data you want to process are in your "Col 4" only. If you need to include the other columns, simply push them also onto the array.

BEWARE: Untested code!

I am just trying to put something together for you to look at right now, l know what is must look like but this is something l have written but im just struggling with the workings on this one. Give me a moment to knock something together based on my previous attenpts.