CODEWITHSUNDEEP
perl
eclare
eclare

Reputation: 139

How to compare relative location within an array?

I'm using the Graph package to create a graph with four vertices, like this:

my $graph = Graph->new;
$graph->add_edges(qw(a b c d));

I want to cycle through all possible combinations of two vertices, which I'm doing with a nested loop.

for my $i ($graph->vertices()){
  for my $j ($graph->vertices()) {
    (statement[s])
  }
}

However, this results in many duplicates, such as for (a, b) and (b, a). To fix this, I would like to have a statement such that the second for loop only runs if $i is earlier in the list than $j. These aren't numbers, so a statement like if($i < $j) does not work. But the program moves through the list in the same order. How do I refer to this order, or set an order and refer to it?

Edit: This might work if there is a way to compare indices of arrays in for loop. I'm not sure if this is possible, though.

Here is the full nested for-loop using the code given in the answer below.

use strict;
use warnings;
use Graph;

my $graph = Graph->new;
$graph->add_edges(qw(a b c d));
my @vertices = $graph->vertices();

for my $i (0..$#vertices) {
    my $vi = $vertices[$i];
    for my $j ($i+1..$#vertices) {
        my $vj = $vertices[$j];
        my $graph = Graph->new;
        $graph->add_edges(qw(a b c d));
        my @vertices = $graph->vertices();
        $graph->add_edge("$i", "v");
        $graph->add_edge("$j", "v");
        $graph->delete_edge("$i", "$j");
        print $graph, "\n";
     }
}

Upvotes: 1

Views: 106

Answers (1)

Chris Charley
Chris Charley

Reputation: 6573

Just read all the vertices into an array, then set up your nested loop.

my @vertices = $graph->vertices();

for my $i (0..$#vertices) {
    my $vi = $vertices[$i]; 
    for my $j ($i+1..$#vertices) {
        my $vj = $vertices[$j];
        ...
     }
}

UPDATE: User said he's getting the output below

 0-v,1-v,a-b,c-d;
 0-v,2-v,a-b,c-d;
 0-v,3-v,a-b,c-d;
 1-v,2-v,a-b,c-d;
 1-v,3-v,a-b,c-d;
 2-v,3-v,a-b,c-d

Upvotes: 1

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