Is this a correct use of map?

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

Oh wise and knowledgeable monks. I seek your wisdom in this hopefully interesting dilemma (ok, enough of that ...). I'm trying to split an array of hashes by a timestamp within the list using map. So far here is what I have.

my @prizes = [  {
          'GivenAway' => undef,
          'Breakdown' => '0',
          'Dcode' => '00000',
          'UserId' => '8853',
          'Prize' => '500',
          'Contracts' => [
                           {
                             'Year' => undef,
                             'Make' => undef,
                             'Model' => undef,
                             'Contract' => '1'
                           }
                         ],
          'Type' => 'prizes',
          'Timestamp' => '2005-11-07 11:18:01',
          'WinnerId' => '2026',
          'lineid' => '2026',
          'Count' => '1',
          'Rate' => 'std'
        }];

    my %month = ( '01' => 'January',
                  '02' => 'February',
                  '03' => 'March',
                  '04' => 'April',
                  '05' => 'May',
                  '06' => 'June',
                  '07' => 'July',
                  '08' => 'August',
                  '09' => 'September',
                  '10' => 'October',
                  '11' => 'November',
                  '12' => 'December',
                  );

my @mapped_prizes = map +{ $month{(split(/-| /,$_->{'Timestamp'}))[1]}
+ => $_ } , @prizes;

## Which hopefully yields
'November' => [{
          'GivenAway' => undef,
          'Breakdown' => '0',
          'Dcode' => '00000',
          'UserId' => '8853',
          'Prize' => '500',
          'Contracts' => [
                           {
                             'Year' => undef,
                             'Make' => undef,
                             'Model' => undef,
                             'Contract' => '1'
                           }
                         ],
          'Type' => 'prizes',
          'Timestamp' => '2005-11-07 11:18:01',
          'WinnerId' => '2026',
          'lineid' => '2026',
          'Count' => '1',
          'Rate' => 'std'},
];
[download]

Sorry about the formatting. I did the best I can with the room I had. Hopefully you get the idea of what I wanted to do. I'm not sure if I should use map +{ } or map +( ). In any case, dumping @mapped_prizes only results in confusion as I'm not sure if its doing what I want it to do. With map +{} Dumper() yields

######MAPPED PRIZES######
$VAR1 = {
          'November' => {
                          'GivenAway' => undef,
                          'Breakdown' => '0',
                          'Dcode' => '00000',
                          'UserId' => '8853',
                          'Prize' => '500',
                          'Contracts' => [
                                           {
                                             'Year' => undef,
                                             'Make' => undef,
                                             'Model' => undef,
                                             'Contract' => '1'
                                           }
                                         ],
                          'Type' => 'prizes',
                          'Timestamp' => '2005-11-07 11:18:01',
                          'WinnerId' => '2026',
                          'lineid' => '2026',
                          'Count' => '1',
                          'Rate' => 'std'
                        }
        };
$VAR2 = {
          'November' => {
                          'GivenAway' => undef,
                          'Breakdown' => '0',
                          'Dcode' => '00000',
                          'UserId' => '8853',
                          'Prize' => '300',
                          'Contracts' => [
                                           {
                                             'Year' => undef,
                                             'Make' => undef,
                                             'Model' => undef,
                                             'Contract' => '100'
                                           }
                                         ],
                          'Type' => 'prizes',
                          'Timestamp' => '2005-11-07 15:06:39',
                          'WinnerId' => '2027',
                          'lineid' => '2027',
                          'Count' => '1',
                          'Rate' => 'std'
                        }
        };
[download]

And with map +() Dumper() yields:

######MAPPED PRIZES######
$VAR1 = 'November';
$VAR2 = {
          'GivenAway' => undef,
          'Breakdown' => '0',
          'Dcode' => '00000',
          'UserId' => '8853',
          'Prize' => '500',
          'Contracts' => [
                           {
                             'Year' => undef,
                             'Make' => undef,
                             'Model' => undef,
                             'Contract' => '1'
                           }
                         ],
          'Type' => 'prizes',
          'Timestamp' => '2005-11-07 11:18:01',
          'WinnerId' => '2026',
          'lineid' => '2026',
          'Count' => '1',
          'Rate' => 'std'
        };
$VAR3 = 'November';
$VAR4 = {
          'GivenAway' => undef,
          'Breakdown' => '0',
          'Dcode' => '00000',
          'UserId' => '8853',
          'Prize' => '300',
          'Contracts' => [
                           {
                             'Year' => undef,
                             'Make' => undef,
                             'Model' => undef,
                             'Contract' => '100'
                           }
                         ],
          'Type' => 'prizes',
          'Timestamp' => '2005-11-07 15:06:39',
          'WinnerId' => '2027',
          'lineid' => '2027',
          'Count' => '1',
          'Rate' => 'std'
        };
[download]

Clever use of map? Or a clever shot in the foot? My thanks, BMaximus

BMaximus

Comment on Is this a correct use of map? Select or Download Code

Replies are listed 'Best First'.
Re: Is this a correct use of map? by Aristotle (Chancellor) on Nov 08, 2005 at 00:04 UTC
I think you want `+()` or `{}`, but not `+{}`. With `+{}`, you will get one hashref per element – whereas I think you want a single hash, in which case you want either an expression (`+()`) or a single-expression block (`{}`). But I can only guess. Other than that confusion, your map is fine, if a little hard to read. I’d put the month extraction code in a subroutine so I could give it a descriptive name. Rather than: `my @mapped_prizes = map +{ $month{(split(/-\| /,$_->{'Timestamp'}))[1]} + => $_ }, @prizes;` [download] I’d write: `sub month_from_datetime { my ( $datetime ) = @_; ( split m{-\| }, $datetime )[1] } my %month_name = ( # ... ); my %mapped_prizes = map { my $month_num = month_from_datetime $_->{'Timestamp'}; $month_name{ $month_num } => $_; }, @prizes;` [download] which makes it quite obvious what’s going on. Makeshifts last the longest.	[reply] [d/l] [select]
Re: Is this a correct use of map? by GrandFather (Saint) on Nov 07, 2005 at 23:41 UTC
Have you run this with `use warnings; use strict;`? When I do I get: `Pseudo-hashes are deprecated at noname2.pl line 41. Argument "2005-11-07 11:18:01" isn't numeric in hash element at noname +2.pl line 41. Use of uninitialized value in split at noname2.pl line 41. Use of uninitialized value in hash element at noname2.pl line 41. Use of uninitialized value in anonymous hash ({}) at noname2.pl line 4 +1.` [download] which sort of indicates a problem. Note that this happens even if I replace the undef values with values. Perl is Huffman encoded by design.	[reply] [d/l] [select]
Re^2: Is this a correct use of map? by BMaximus (Chaplain) on Nov 07, 2005 at 23:53 UTC
I have `use warnings; use strict;` on and I get no errors or warnings probably because its just a small snippet of a bigger picture that I tried to shrink so I wouldn't bore you with the rest of the code. I'm looking to see if I created the right block to do what I put at the bottom of the code. I guess if it can't be run it really down't help explain what needs to be done. I tried my best to explain. Unfortunately it wasn't good enough. BMaximus	[reply] [d/l]
Re^3: Is this a correct use of map? by GrandFather (Saint) on Nov 08, 2005 at 00:09 UTC
Try altering the following code to show your problem if it doesn't do what you are trying to achieve already: use strict; use warnings; use Data::Dumper; my @prizes = ( { 'Timestamp' => '2005-11-07 11:18:01', 'WinnerId' => '2026', 'lineid' => '2026', }, { 'Timestamp' => '2005-01-07 11:18:01', 'WinnerId' => '2001', 'lineid' => '2001', }, { 'Timestamp' => '2005-05-07 11:18:01', 'WinnerId' => '2015', 'lineid' => '2015', }, ); my %month = ( '01' => 'January', '02' => 'February', '03' => 'March', '04' => 'April', '05' => 'May', '06' => 'June', '07' => 'July', '08' => 'August', '09' => 'September', '10' => 'October', '11' => 'November', '12' => 'December', ); my @mapped_prizes = map {[$month{(split (/-/, $_->{'Timestamp'}))[1]} +=> $_]} @prizes; print Dumper (\@mapped_prizes); [download] Prints: `$VAR1 = [ [ 'November', { 'Timestamp' => '2005-11-07 11:18:01', 'lineid' => '2026', 'WinnerId' => '2026' } ], [ 'January', { 'Timestamp' => '2005-01-07 11:18:01', 'lineid' => '2001', 'WinnerId' => '2001' } ], [ 'May', { 'Timestamp' => '2005-05-07 11:18:01', 'lineid' => '2015', 'WinnerId' => '2015' } ] ];` [download] Note that I removed some of the fields from the hash - only a couple are needed to demonstrate the issue. Note also that I added a couple of entries because it seems that more than one is required to show the issue. And further, note that I reduced the reference nesting by a level in the @prizes array which cleans up the warnings that I was seeing and also that I changed the +{}, in your original map (that looks rather peculiar) to a more usual {} and altered the contents of the map expression to do what I guess you want to do: generate an list of pairs of month and prize elements. I don't see why you don't want this as a hash however. Perl is Huffman encoded by design.	[reply] [d/l] [select]


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