Perhaps keep an index to the original data hash, thusly:

use strict;

## simulate original %data hash
my %data = map { (int(rand(10**10) + 10**9) => rand } (0 .. 2*10**5);

my ($keys, $values) = ([], []);   ## remember what goes where
foreach (sort keys %data) {
  push @$keys, $_;
  push @$values, $data{$_};
}

## now obtain rolling averages
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