I hope my explanation is ok. :)

:) I wanted to hear something more basic, what you described is like a statement of goals

Consider this loop

for $one ( 1 .. 10 ){
    for $two ( 1 .. 10 ){
        
    }
}
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Please can you describe what it does?

Using nested for loop to compare all elements in the array to each other?

Ok, thank you,

Ok, second take, lets try like this , slightly less socratic, trying not to figure out where you're stuck, but pretending as if this is your first step in solving this problem, and you're using computer instead of pencil and paper

Please fill in the blanks in program below , edit sub UsedToBeJustDoWork

Create however many variables you need, change whatever names you want, in the end the program should run and produce the data structure you want your program to have

you should not use foreach or while, just type out the vars and math you need to get the correct by your definition of $final_output_wanted

#!/usr/bin/perl --
use strict; use warnings;
use Data::Dump qw/ dd /;
Main( @ARGV );
exit( 0 );
sub Main {
    UsedToBeJustDoWork();
}
sub UsedToBeJustDoWork {
    my $full_data = [
      ["M11", 0.1, 10, 24, 56, 77, 98, 72],
      ["M12", 0.3, 13, 44, 23, 45, 56, 11],
      ["M13", 0.4, 54, 23, 11, 25, 67, 91],
    ];
    
    
    my $d_to_h = [
      [ 24, 56, 77, 98, 72],
      [ 44, 23, 45, 56, 11],
      [ 23, 11, 25, 67, 91],
    ];
    
## I don't know what you want here
    my $these_first_row_average = $d_to_h->[0] + $d_to_h->[1] + $d_to_
+h->[2] + $d_to_h->[3] + $d_to_h->[4] / 4;
    
    my $final_output_wanted = [
## I don't know what you want here
        $these_first,
        $these_second,
        $these_third,
    ];
    dd( $final_output_wanted );
}
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