Geez! What a lot of non-answers for a simple question.

#! perl -slw
use strict;
use Data::Dump qw[ pp ];

my @data = (
    {"name"=>"joe","age"=>21,"weight"=>150,"height"=>"","sex"=>""},
    {"name"=>"joe","age"=>"","weight"=>"","height"=>"6'0","sex"=>""},
    {"name"=>"joe","age"=>"21","weight"=>"","height"=>"","sex"=>"male"
+},
);

my %full;

for my $p ( @data ) {
    $full{ $_ } ||= $p->{ $_ } for keys %$p;
}

pp \%full;

__END__
c:\test>junk17
{ age => 21, height => "6'0", name => "joe", sex => "male", weight => 
+150 }
[download]

jjw92:

Just a minor quibble: I wouldn't use empty strings to signify missing values. I use the default undef value for that (and in a hash, I'll often not insert the key for a missing value, either). In the general case, you may find that an empty string is a legitimate value, and then you wouldn't be able to tell the difference between a missing value and an intentional empty string.

In the case you've presented, it appears that it wouldn't matter, as an empty string wouldn't normally be a valid value for age, height, weight or sex. But if you had a "nickname" field, for instance, a person with no nickname might be represented with an empty string. So if one of your data sources doesn't provide a nickname, stuffing the nickname with empty strings would imply to your database that those people have no nickname.

Why would it matter? Think of three questions: (1) How many people in your database have nicknames? (2) How many people don't have nicknames? (3) How many people have we asked?

Your method would allow you to answer question 1--mostly. But you couldn't legitimately answer questions 2 or 3. Using undef vs. and empty string would let you answer questions 2 and 3, as well as give you a better answer for question 1 (Out of X people that we've asked, Y have a nickname).

Another way it could matter: In the problem you're solving now, you're merging information from multiple records. If one record is missing a data item, you can overlay the missing field from the other record. But what do you do if there's a conflict between two data items? You'll need to figure out how to resolve those differences. Throw in the fact that a nickname may be explicitly blank, and your code wouldn't be able to tell that the person no longer uses a nickname. Instead, they'll be stuck with their old nickname since you wouldn't be able to overlay it with an empty string--it would be treated as a missing value and ignored...

Sorry for the long, rambling node. I haven't the time to make it short and concise.

...roboticus

I see the merit in this, but it isn't really applicable in this case. I just made these hashes/keys/values off of what I could think of on the spot. What I am actually dealing with is an array of hashes returned by slurping a .csv file. This leads me to the statement that every field with no data will be a void, "", and every piece of data will correspond to the correct header. I like the thought though, and it certainly would apply in many other cases. Thanks for the response.

my %h;
@h{keys %$_} = values %$_ for @data;
[download]

[I]t does not check for ... several different values for a [key] ...

... or for identical values for the same key in different anonymous hashes when those values are the empty string, as most values are in the example data.

Covered by "etc" ;)

When trying that, it only works for storing the last hash. If I knew more about what it was doing, maybe it is just a formatting issue? I'm not sure..

As AnomalousMonk noted, you would have to avoid setting the empty values. But as I noted, you should rather not use this approach.

Great, you have a goal, now simply lay out the steps to accomplish that goal, translate that to code, and you're finished :) How (Not) To Ask A Question.

Sorry for all the backslashed double-quotes:

>perl -wMstrict -le
"my @data = (
   { \"name\" => \"joe\",
     \"age\" => 21,
     \"weight\" => 150,
     \"height\" => \"\",
     \"sex\" => \"\",
     },
   { \"name\" => \"joe\",
     \"age\" => \"\",
     \"weight\" => \"\",
     \"height\" => \"6'0\",
     \"sex\" => \"\",
     },
   { \"name\" => \"joe\",
      \"age\" => \"21\",
      \"weight\" => \"\",
      \"height\" => \"\",
      \"sex\" => \"male\",
      },
   );
 my %hash =
   map {
     my $hr = $_;
     map  { $_, $hr->{$_} }
     grep $hr->{$_} ne '',
     keys %$hr
     }
   @data
   ;
 use Data::Dumper;
 print Dumper \%hash;
"
$VAR1 = {
          'name' => 'joe',
          'weight' => 150,
          'sex' => 'male',
          'height' => '6\'0',
          'age' => '21'
        };
[download]

I am still in the process of learning Perl. Could you please explain to me what is actually happening with the map{} process?

See also: Map: The Basics

HTH,

planetscape

See map.