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@data_out = uniq(@sorted_data);

...
    return (uniq(@xs)) if grep {substr($x,0,7) eq substr($_,0,7)} @xs;
    return ($x,uniq(@xs));
}

foreach (reverse @sorted_data) {
    unshift(@data_out, $_) unless ($seen{substr($_,0,7)}++);
}

@data_out = nub(@sorted_data);

...
    return $x unless @xs;
    return (nub(grep {substr($x,0,7) ne substr($_,0,7)} @xs), $x);
}