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Re: SQL like query over iterable in perl (updated x2)

by haukex (Bishop)
on Mar 02, 2017 at 07:25 UTC ( #1183355=note: print w/replies, xml ) Need Help??

in reply to SQL like query over iterable in perl

Sounds to me like foreach (and perhaps map) and hashes will help you:

my @array_of_objects = ( { sex=>'Male', occupation=>'foo' }, { sex=>'Female', occupation=>'foo' }, { sex=>'Male', occupation=>'bar' }, { sex=>'Female', occupation=>'bar' }, { sex=>'Female', occupation=>'foo' }, ); my %counts; $counts{ $_->{sex} }++ for @array_of_objects; my %grouped; $grouped{ $_->{sex} }{ $_->{occupation} }++ for @array_of_objects; use Data::Dumper; print Dumper( \%counts, \%grouped ); __END__ $VAR1 = { 'Female' => 3, 'Male' => 2 }; $VAR2 = { 'Female' => { 'bar' => 1, 'foo' => 2 }, 'Male' => { 'foo' => 1, 'bar' => 1 } };

Update: Personally, I'd prefer the above, but if you really want a generic function, here's one option. Probably not the most efficient solution because it's recursive, I don't think the morning caffeine has fully kicked in yet ;-) Input and output is the same as above. (Update: huck's solution, posted before the below, is the non-recursive variation of this.)

sub count { my ($data, $fields) = @_; $fields = [$fields] unless ref $fields; my $count = {}; _dive( $count, $_, @$fields ) for @$data; return $count; } sub _dive { my ($ref, $obj, @path) = @_; my $targ = \$ref->{ $obj->{ shift @path } }; if (!@path) { $$targ++; return $ref } $$targ = _dive( $$targ, $obj, @path ); } print Dumper( count(\@array_of_objects, 'sex') ); print Dumper( count(\@array_of_objects, ['sex','occupation']) );

Update 2: In the above, I'm working with hash references instead of objects. If you want to use real objects and method calls, then in the first example, replace { $_->{sex} }{ $_->{occupation} } with { $_->sex }{ $_->occupation }, and in the second example, replace $obj->{ shift @path } with $obj->${\shift @path}.

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