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Re^2: extracting elements by key from an array of hashes

by Athanasius (Archbishop)
on Sep 25, 2015 at 13:25 UTC ( [id://1143013]=note: print w/replies, xml ) Need Help??


in reply to Re: extracting elements by key from an array of hashes
in thread extracting elements by key from an array of hashes

Hello Discipulus,

grep defined, map {$_->{'k2'}} @aoh;

This works well as long as the hash value is itself defined. But if the hash entry exists with a value of undef:

my @aoh =
(
    { k0 => 'v0'  },
    { k1 => 'v1'  },
    { k2 => undef },
    { k3 => 'v3'  },
);

[download]

then the result of the grep will be indistinguishable from the case in which the hash entry does not exist at all. The following does distinguish between these two cases:

map { exists $_->{k2} ? $_->{k2} : () } @aoh;

[download]

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

Replies are listed 'Best First'.
Re^3: extracting elements by key from an array of hashes
by mr_ron (Chaplain) on Sep 26, 2015 at 00:52 UTC
    Another cleaner variant that works with the initial data structure. 
    my @aoh = ( 
    {k0 => 'v0' }
  , {k1 => 'v1' }
  , {k2 => 'v2' }
  , {k3 => 'v3' }
);

my ($val) = grep {exists $_->{k2}} @aoh;
$val &&= $val->{k2};

    [download]
[reply]
[d/l]
Re^3: extracting elements by key from an array of hashes
by Discipulus (Canon) on Sep 25, 2015 at 19:24 UTC
    yes, i was aware of that possibility. thanks for your code. Perl can be incredibly expressive!

    L*
    There are no rules, there are no thumbs..
    Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
[reply]
[d/l]

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