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copying array of hashes

Posted on 2009-05-10
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Last Modified: 2012-05-06
how can I make a copy of an array of hashes so that the original one isn't affected? I don't have use storage in my PERL version
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Question by:cucugirl
6 Comments
 
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by:
ozo earned 84 total points
ID: 24349370
@array=({k1=>'v1',k2=>'v2'},{k1=>'v1',k2=>'v2'});
@copy=map{{%$_}}@array;
$copy[1]{k2}++;
print "$copy[1]{k2} $array[1]{k2}\n";
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by:Adam314
ID: 24351547
>>I don't have use storage
I'm assuming you meant you don't have the Storable module?  If so, can you install it?  Have you tried?  Did you get an error?
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by:vikaskhoria
vikaskhoria earned 83 total points
ID: 24352113
Check my script below:
(This deletes elements from the hash and the original hash is modified to the desired hash)

Thanks,
Vikas.

#!/usr/bin/perl
 
my %my_hash = ('TEST' =>'T' ,'QUIZ'=>'4','HWORK'=>'3');
my @table = ( {'TEST'=>'T'}, {'TEST'=>'F'},{'QUIZ'=>'1'},{'QUIZ'=> '2'},{'HWORK'=>'3'}, {'HWORK'=>'3'});
 
for my $value (keys %my_hash)
{
        my $found = 0;
        foreach $i (0 .. @table-1)
        {
                if ( $table[$i]{$value} == $my_hash{$value} ) {
                        $found = 1;
                }
        }
        if ( ! $found )
        {
                delete($my_hash{$value});
        }
}

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by:vikaskhoria
ID: 24361590
Check this link below:
http://www.perlmonks.org/?node_id=93693

This talks about copying array of hashes.
This may be of some help to you.
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Assisted Solution

by:wilcoxon
wilcoxon earned 83 total points
ID: 25953183
The best way is to use Clone (this handles any level of nested structures).  Alternately, if you know that the hashes only contain scalars, it's easy to copy them manually.
my $orig = [{first=>1,second=>2},{first=>3,second=>4}]; 
# using Clone
use Clone qw(clone);
my $copy = clone($orig); 
# manually copying
## slow/inefficient way
my $copy = [];
foreach my $el (@$orig) {
    my %tmp;
    foreach my $key (%$el) {
        $tmp{$key} = $el->{$key};
    }
    push @$copy, {%tmp};
}
## better way
my $copy = [];
foreach my $el (@$orig) {
    push @$copy, {%$el};
}
## ozo's way - more succinct but should be about same performance (I think)
my $copy = [map { {%$_} } @$orig];

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