In search of elegant code - looking deeply into a hash

davidfilmer has asked for the wisdom of the Perl Monks concerning the following question:

Masters - Suppose I have a hash like this:

my %uid =(
   1 => {
      'firstname' => 'Alice',
      'lastname'  => 'Foo',
   },
   2 => {
      'firstname' => 'Bob',
      'lastname'  => 'Bar',
   },
);
[download]

I want to find out Alice's last name. Of course, I could just slog through the hash:

foreach my $key( keys %uid ){
   if( $uid{$key}{'firstname'} eq 'Alice' ){
      print "lastname is $uid{$key}{'lastname'}\n";
   }
}
[download]

But that seems inelegant. Is there a more elegant way?

Comment on In search of elegant code - looking deeply into a hash Select or Download Code

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Re: In search of elegant code - looking deeply into a hash by NetWallah (Canon) on Mar 02, 2016 at 03:49 UTC
How about this: `my @possible_last_names = map {$_->{lastname}} grep {$_->{firstname} eq "Alice"} values %uid; # Returns ("Foo")` [download] "Think of how stupid the average person is, and realize half of them are stupider than that." - George Carlin	[reply] [d/l]
Re: In search of elegant code - looking deeply into a hash by beech (Parson) on Mar 02, 2016 at 03:13 UTC
But that seems inelegant. Is there a more elegant way? Yes, wrap it in a sub `if( my $lastname = uid_lastname( \%uid, 'Alice' ) ){ print "lastname is $lastname\n"; }` [download] Read more... (577 Bytes) Other "elegant" options might include Data::Diver , Data::DPath, Data::Path/Data::Path update: with dpath you can lookup the lastname like so `my $lastname = dpath( q{//firstname[ value =~ /Alice/i ]/../lastname} + )->match( \%uid ) my $lastname = dpath( q{//firstname/.[ value eq 'Alice' ]/../lastname +} )->match( \%uid ) ;` [download]	[reply] [d/l] [select]
Re: In search of elegant code - looking deeply into a hash by Laurent_R (Canon) on Mar 02, 2016 at 07:26 UTC
The issue is not so much that the code is "inelegant", but that the data structure is not well adapter to your query. Perhaps you should rethink the data structure. Or, if you can't and if you have to do that often, then add a lookup table with the first names as the key and a list of records as a value. This will take some time to build but make queries faster and easier thereafter.	[reply]
Re: In search of elegant code - looking deeply into a hash by flowdy (Scribe) on Mar 02, 2016 at 12:18 UTC
Certainly depending on what you want to do, you should also consider using a database, at least SQLite that does not require a running database server, in favour of implementing a little quick-and-dirty database engine like this. It is much more scalable. This at least would deserve the attribute "elegant" in my eyes, given your example code that suggests expansion to other data associated with those people.	[reply]
Re: In search of elegant code - looking deeply into a hash by Anonymous Monk on Mar 02, 2016 at 13:25 UTC
More concise, or just more obfuscated? `print +{map @$_{qw(firstname lastname)}, values %uid}->{Alice};` [download]	[reply] [d/l]