Perl: Changing values of a dynamic array reference

Question

Assume you have:

my $data1 = [
  +{ id => 1, name => 'A' },
  +{ id => 2, name => 'B' },
  +{ id => 3, name => 'C' },
  +{ id => 4, name => 'A' },
  # .... many rows
];

as input.

I want to change id to 1 (id =>1 ) every time name is 'A'(name => 'A'). Is a loop totally necessary?

    #  loop

    if ( $data1->[#what to put here?]->{id} = 1 ) {
        $data1->[#what to put here?]->{name} = 'A';
    }

How to do this?

marderh · Accepted Answer · 2013-08-22 09:38:03Z

2

Here is an example of how to loop through your datastructure. I used Data::Dumper to look into them. It should make clear how it is structured.

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $data1 = [{ id => 1, name => 'A' },{ id => 2, name => 'B' },{ id => 3, name => 'C' },{ id => 4, name => 'A' },];

print "Before: \n" . Data::Dumper->Dump($data1)."\n\n";

foreach (@$data1){
    if ($_->{name} eq 'A'){
        $_->{id} = 1;
    }
}

print "After: \n" . Data::Dumper->Dump($data1)."\n";

Your $data1 is an array-reference. Its dereferenced (@$data1) so we can loop through it with foreach and access the hashes within. As we're still using the refenrences we edit them "in place".

answered Aug 22, 2013 at 9:38

marderh

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Comments

jvverde · Accepted Answer · 2013-08-22 09:42:04Z

2

Well you can use a map

map {$_->{id} = 1 if $_->{name} eq 'A'} @$data1;

but it is a loop too.

answered Aug 22, 2013 at 9:42

jvverde

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2 Comments

marderh Over a year ago

Should be @$data1 instead of @data1

jvverde Over a year ago

@marderh Sorry. I forget it.

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