Re^2: SQL like query over iterable in perl

More generic than haukex's, more pure-perl than Athanasius's, more functional than OO

Shorter than huck's ;-P

sub count {
    my ($data, $fields) = @_;
    $fields = [$fields] unless ref $fields;
    my $count = {};
    for my $obj (@$data) {
        my $ref = $count;
        $ref = $ref->{ $obj->{ $fields->[$_] } } //= {}
            for 0..$#$fields-1;
        $ref->{ $obj->{ $fields->[-1] } }++;
    }
    return $count;
}
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(For input, output and other context see my other node)

Comment on Re^2: SQL like query over iterable in perl Download Code

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Re^3: SQL like query over iterable in perl by huck (Prior) on Mar 02, 2017 at 09:30 UTC
Cute Made me think `$fields = [$fields,@_] unless ref fields;` and not that it matters here, and i would have to look up funny debug commands to tell for sure, but are `$#$fields-1` and `$fields->[-1]` optimized or does the subtraction happen every loop of $obj? Im never sure. and in mine, besides $data,$fields,and $count as nicer variable names, i had already decided i should have $size1 be named as $nterminal and $size2 named as $nsubparts to make it clearer what they did. wasnt gun'a post as a "fix" but this gave me an excuse to mention it. Edited to add: What about missing fields? ~~`$ref = $ref->{ $obj->{ $fields->[$_] // '.' } } //= {}`~~ where '.' is used like the SAS missing variable. That wasnt right, instead `$ref = $ref->{ $obj->{ $fields->[$_] } // '.' } //= {}`	[reply] [d/l] [select]
Re^4: SQL like query over iterable in perl by haukex (Archbishop) on Mar 02, 2017 at 13:06 UTC
I hope it's clear I wasn't being entirely serious or saying that my code was "better", it was just a lighthearted retort :-) i would have to look up funny debug commands to tell for sure, but are `$#$fields-1` and `$fields->[-1]` optimized or does the subtraction happen every loop I'm not sure either, but I'd have to guess no, since the optimizer would have to know for certain that `@fields` won't change, and in a language as dynamic as Perl, that's probably very rarely the case, if ever. As for the debug command, I assume you're thinking of B::Deparse, invoked as `perl -MO=Deparse script.pl`, which would show, for example, constant folding. I did a quick test with Benchmark and refactored out `$fields->[-1]` and `$#$fields-1` to before the loop, and that gave a consistent but small speed increase of ~5% (although IIRC, in terms of Benchmark results that's still in the margin of error of being insignificant). I didn't take missing fields into account because the OP was asking about objects, but you have a good point there, my code doesn't properly handle `undef` values (or an empty `@$fields` for that matter).	[reply] [d/l] [select]
Re^4: SQL like query over iterable in perl by pwagyi (Monk) on Mar 04, 2017 at 03:33 UTC
Actually I have quite similar function that dynamically creates nested hash counter. That gives confirmation that I'm in the right direction. :) Thanks.	[reply]


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