What about making a subroutine for the iterative comparison and have it recursively call itself on the kept values from the array unless some condition is true?

iterate(@entries);

sub iterate {
    my ( $top_entry, @entries ) = @_;
    my @keepers;

    for (@entries) {
        my $comparison = compare_sub( $top_entry, $_ );
        if ( $comparison > $user_defined_value ) {
            push @keepers, $_;
        }
    }

    iterate(@keepers) unless ...;
}
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EDIT: A variation where you continue iterating or assign final result depending on some condition. It's hard to know the right approach from here w/o more info

my @final_result;
iterate(@entries);

sub iterate {
    my ( $top_entry, @entries ) = @_;
    my @keepers;

    for (@entries) {
        my $comparison = compare_sub( $top_entry, $_ );
        if ( $comparison > $user_defined_value ) {
            push @keepers, $_;
        }
    }

    if (...) {
        iterate(@keepers);
    }
    else {
        @final_result = ...;
    }
}
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