Efficiently process all possible 2D array combinations in Perl

Question

I have a 2D array containing numbers. I am attempting to work out the product of multiplying a single number from each sub-array with one from each of the other sub-arrays; I then need to do this for all possible combinations. The aim is that I input a file of the frequency of individual events, and get an output of the probability of a particular series of these events happening, with one event from each set. I have fudged together some code with the help of a previous question: ``` for my $aref ( getCartesian(@freq) ) { my $p = 1; foreach my $n (@$aref) { $p = $p * $n; } print "$p
"; } sub getCartesian { my @input = @_; my @ret = map [$_], @{ shift @input }; for my $a2 (@input) { @ret = map { my $v = $_; map [@$v, $_], @$a2; } @ret; } return @ret; } ``` where `@freq` is an array of arrays, such as: ``` @freq = [0.1, 0.2, 0.3,] [0.4, 0.5, 0.6,] [0.7, 0.8, 0.9,]; `and ~ 20 more sub arrays` ``` This works fine for a small test file, but when I give it my required input of 24 sub-array…

Accepted Answer

Set::CrossProduct lets you iterate through the Cartesian product so you don't have to store everything in memory:

```
use List::Util qw(reduce);
use Set::CrossProduct;

my @array = (
    [0.1, 0.2, 0.3],
    [0.4, 0.5, 0.6],
    [0.7, 0.8, 0.9]
);

my $iterator = Set::CrossProduct->new(\@array);
while (my $tuple = $iterator->get) {
    say '(', join(', ', @$tuple), '): ', reduce { $a * $b } @$tuple;
}
```

Outputs:

```
(0.1, 0.4, 0.7): 0.028
(0.1, 0.4, 0.8): 0.032
(0.1, 0.4, 0.9): 0.036
(0.1, 0.5, 0.7): 0.035
(0.1, 0.5, 0.8): 0.04
(0.1, 0.5, 0.9): 0.045
(0.1, 0.6, 0.7): 0.042
(0.1, 0.6, 0.8): 0.048
(0.1, 0.6, 0.9): 0.054
(0.2, 0.4, 0.7): 0.056
(0.2, 0.4, 0.8): 0.064
(0.2, 0.4, 0.9): 0.072
(0.2, 0.5, 0.7): 0.07
(0.2, 0.5, 0.8): 0.08
(0.2, 0.5, 0.9): 0.09
(0.2, 0.6, 0.7): 0.084
(0.2, 0.6, 0.8): 0.096
(0.2, 0.6, 0.9): 0.108
(0.3, 0.4, 0.7): 0.084
(0.3, 0.4, 0.8): 0.096
(0.3, 0.4, 0.9): 0.108
(0.3, 0.5, 0.7): 0.105
(0.3, 0.5, 0.8): 0.12
(0.3, 0.5, 0.9): 0.135
(0.3, 0.6, 0.7): 0.126
(0.3, 0.6, 0.8): 0.144
(0.3, 0.6, 0.9): 0.162
```

Efficiently process all possible 2D array combinations in Perl

Solution

Problem

Related problems