#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

my %parent = (
    'file3232.ext' => {
        e => 0,
        k => '0.0031',
        i => '26.9',
        j => '33.0',
    }
);

my %returned = (
    'file3232.ext'  => {
        e => 0,
        k => '0.1040',
        i => '26.7',
        j => '14.6',
    }
);

for my $file (keys %returned) {
    for my $dataset (keys %{ $returned{$file} }) {
        $parent{$file}{$dataset} += $returned{$file}{$dataset};
    }
}

print Dumper \%parent;