CODEWITHSUNDEEP
arraysperllistloops
XeroG
XeroG

Reputation: 37

Print a List of Arrays in Perl?

I am attempting write code that will allow me to print a list of arrays in Perl.

I have a list of arrays of GPS coordinates called @points that is formatted with arrays of lat/lon like so:

@points = [34.2,17.5],[-64.1, 110.35],[54.8,77.1], and so on and so forth

I am able to print the list itself using print "$_\n" for @points;, however this only gives me the memory reference for the array. I know that you can't just print arrays like you can strings or integers however I am stuck on how to actually iterate through the list and print the integers. I tried using a foreach loop and @_ to print at each increment however that didn't work for me either. If anyone is able to give me any direction on this it would be greatly appreciated.

Upvotes: 0

Views: 465

Answers (4)

AbhiNickz
AbhiNickz

Reputation: 1093

One More solution for this, although I changed @points to reference.

use strict;
use warnings;
my $points = [[34.2,17.5],[-64.1, 110.35],[54.8,77.1]];

for(my $i = 0; $i<=6; $i++)
{
    print $points->[$i]->[0];
    print "\n";
    print $points->[$i]->[1];
    print "\n";
}

Upvotes: 0

Miguel Prz
Miguel Prz

Reputation: 13792

You may use the Data::Dumper CPAN module, it's simple:

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

my @points = ( [34.2,17.5], [-64.1, 110.35], [54.8,77.1] );
$Data::Dumper::Terse = 1;
print Dumper(\@points), "\n";

#---> prints:
[
  [
    '34.2',
    '17.5'
  ],
  [
    '-64.1',
    '110.35'
  ],
  [
    '54.8',
    '77.1'
  ]
]

Upvotes: 1

Sobrique
Sobrique

Reputation: 53478

You're doing two dimensional iteration so you need a two dimensional loop. The way perl does two dimensional data structures is via references.

In your example - @points isn't a 2d structure, it's a list of references - which is why if you print it you get:

print "@points";

Gives:

ARRAY(0x4a6dec) ARRAY(0x4a6fb4) ARRAY(0x12fef64)

So you need to dereference each of those elements. There's several ways to do this, but essentially @{$reference} is how it works.

There are a few ways of accomplishing the task, but essentially:

foreach my $group ( @points ) { 
    print join ("\n", @$group ),"\n"; 
}

For example - join is one iterate, foreach is another. (Note - @$group and @{$group} mean the same thing, so you don't need the braces. If you were trying to do @$group[1] you would need it, to disambiguate whether you were after @{$group[1]} or @{$group}[1])

Or for another:

use feature qw ( say );
say for map { @$_ } @points;

This is making use of the fact that map is applying a transform to each element of @points, and that "transform" is simply "dereference and give me the elements".

Of course, then you have 'smashed flat' @points and not retained their mutual association.

Upvotes: 0

Hunter McMillen
Hunter McMillen

Reputation: 61512

You need to use the @{ ... } sigil to dereference your array references. This will give you a plain array that you can print directly or manipulate with the join builtin to get better formatted output:

use strict;
use warnings;

my @points = ([34.2,17.5],[-64.1, 110.35],[54.8,77.1]);
print join(',', @$_), "\n" foreach my @points;

output:

34.2,17.5
-64.1,110.35
54.8,77.1

You should note that I placed parentheses around your definition of the @points array:

my @points = ([34.2,17.5],[-64.1, 110.35],[54.8,77.1]);

these parentheses are required due to how lists are constructed in Perl, without them present @points would only be assigned the final array reference of [54.8,77.1]

Upvotes: 1

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