Put the data into a single hash structure, and then do the math for your formatting at the very end. Throw in a couple of warnings in case the file processing ends prematurely.

Use List::Util for quick functions to manipulate a list of values.

use List::Util qw(sum max min);

use strict;

my $keysfile = 'keys.txt';
my $valsfile = 'vals.txt';

open(KEYS, $keysfile) or die "Can't open $keysfile: $!";
open(VALS, $valsfile) or die "Can't open $valsfile: $!";

my %data;

while (!eof(KEYS) && !eof(VALS)) {
    chomp(my $key = <KEYS>);
    chomp(my $val = <VALS>);
    
    push @{$data{$key}}, $val;
}

warn "Premature end of $keysfile\n" if !eof(VALS);
warn "Premature end of $valsfile\n" if !eof(KEYS);

foreach my $name (sort keys %data) {
    my $values = $data{$name};

    my $count   = @$values;
    my $total   = sum(@$values);
    my $average = $total / $count;
    my $max     = max(@$values);
    my $min     = min(@$values);
    
    print "$name => total=$total, average=$average, max=$max, min=$min
+\n";
}
[download]

- Miller