Re: Array of Hashes to Hash of arrays for SQL::Abstract

In most cases "better" is likely to be subjective. However, I would probably try to loop over $data just once:

use strict;
use warnings;

use Test::More tests => 1;

my $data = [
  {a => 1, b => 2},
  {a => 3, b => 4},
  {a => 5, b => 6}
];

my $want = {
    a => [1, 3, 5],
    b => [2, 4, 6]
};

my %columns;

for my $row (@$data) {
    for my $k (keys %$row) {
        $columns{$k} //= [];
        push @{$columns{$k}}, $row->{$k};
    }
}

is_deeply \%columns, $want;
[download]

Comment on Re: Array of Hashes to Hash of arrays for SQL::Abstract Download Code

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Re^2: Array of Hashes to Hash of arrays for SQL::Abstract by Skeeve (Parson) on Mar 18, 2020 at 10:39 UTC
However, I would probably try to loop over $data just once The disadvantage here is, that you might loose null-values due to missing keys in your data `my $data = [ {a => 1, b => 2, c => 11}, {a => 3, c => 12}, {a => 5, b => 6} ];` [download] `s$$([},&%#}/&/]+}%&{});#$&&s&&$^X.($'^"%]=\&(\|?{%` `+`.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e	[reply] [d/l] [select]
Re^3: Array of Hashes to Hash of arrays for SQL::Abstract by Veltro (Hermit) on Mar 18, 2020 at 16:27 UTC
I think you are right, in such circumstance I think I would use an index: Something like: `for my $i (0..$#{$data}) { foreach ( keys %{$data->[$i]} ) { $columns->{$_}->[$i] = $data->[$i]->{$_} ; } ; }` [download] Also makes it fairly easy to see what happens: `$columns->{$_}->[$i] = $data->[$i]->{$_} ; hash------^-------------------------^ array-----------^-------------^` [download]	[reply] [d/l] [select]
Re^3: Array of Hashes to Hash of arrays for SQL::Abstract by haukex (Archbishop) on Mar 19, 2020 at 09:52 UTC
The disadvantage here is, that you might loose null-values due to missing keys in your data ... which you didn't mention at all in the root node. Changing the specs on us is not nice :-P Is this example you've shown now representative, or are there other edge cases?	[reply]
Re^4: Array of Hashes to Hash of arrays for SQL::Abstract by Skeeve (Parson) on Mar 19, 2020 at 15:13 UTC
... which you didn't mention at all in the root node You are right. This is because it was obvious to me. I think this happens to every programmer. Sorry. or are there other edge cases None that I know of. `s$$([},&%#}/&/]+}%&{});#$&&s&&$^X.($'^"%]=\&(\|?{%` `+`.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e	[reply] [d/l] [select]