Searching and Shuffling a Perl Array

Using Perl Arrays – Part 4

Perl Course

Foreword: In this part of the series, I explain how to find the first array element for which a condition is true; how to determine if a certain element is found in an array. I also explain how to select a random element from an array and how to shuffle an array randomly.

By: Chrysanthus Date Published: 30 Oct 2015

Introduction

This is part 4 of my series, Using Perl Arrays. In this part of the series, I explain how to find the first array element for which a condition is true; how to determine if a certain element is found in an array. I also explain how to select a random element from an array and how to shuffle an array randomly. You should have read the previous parts of the series before reaching here, as this is a continuation.

First Array element for which a Condition is true
In this section I explain how to find the first array element for which a condition is true. It is simple: just use a foreach loop with regular expression (or some other scheme) to iterate through the array and stop the iteration with the last command, when you see the element. The following code illustrates this; it looks for the first element that has “apple”:

use strict;

    my @fruits = ("pear", "orange", "banana", "pineapple", "lime", "apple", "lemon");

    my $found;
    foreach (@fruits)
        {
            if(/apple/)
                {
                    $found = $_;
                    last;
                }
        }

    print $found;

The output is,

    pineapple

The if-condition in the code is, (/apple/). In a foreach loop, it actually means ($_ =~ /apple/). Instead of identifying the element found, you can identify the index, as the following code shows:

use strict;

    my @fruits = ("pear", "orange", "banana", "pineapple", "lime", "apple", "lemon");

        my( $found, $index ) = ( undef, -1 );

        foreach my $i (0..$#fruits)
            {
                if($fruits[$i] =~ /apple/)
                    {
                        $found = $fruits[$i];
                        $index = $i;
                        last;
                    }
            }

    print "'$found' at index, $index";

The output is:

    'pinapple' at index, 3

Checking if an Element is in an Array
In this section I explain how you can tell whether a certain element is contained in a list or array? It is simple: use the smart match operator. The smart match operator is ~~ . It means, in, in this context. Use it in an if-condition. The if-condition will return true if the item is in the array, or false if the item is not.

use strict;

    my @fruits = ("pear", "orange", "banana", "pineapple", "lime", "apple", "lemon");

    my $item = "lime";

    if($item ~~ @fruits)
        {
            print "$item is in the array.";
        }
    else
        {
            print "$item is not in the array.";
        }

The output is:

    lime is in the array.

This search is case sensitive.

You could have scanned the array with a foreach loop to see if the item is there. However, that would not be mature enough.

Selecting a Random Element from an Array
To select a random element from an array, use the predefined rand() function as follows:

        my $index   = rand @array;
        my $element = $array[$index];

where the random index is first returned and then the index is used to return the element. A shorter form of the above two statements is:

        my $element = $array[rand @array];

Try the following code:

use strict;

    my @fruits = ("pear", "orange", "banana", "pineapple", "lime", "apple", "lemon");

    my $element = $fruits[rand @fruits];

    print $element;

I tried the code in my computer and I had,

    orange

Since it is random, yours will be different.

Shuffling an Array
To shuffle an array, use a module that is installed with Perl as the following code illustrates:

use strict;

use List::Util 'shuffle';

    my @fruits = ("pear", "orange", "banana", "pineapple", "lime", "apple", "lemon");

    my @shuffled = shuffle(@fruits);

    print "$_ " foreach @shuffled;

Note the statement, “use List::Util 'shuffle';” and its function, shuffle() that it brings. I tried the code in my computer and I had:

    orange lime apple pineapple lemon banana pear

Since it is shuffling, your own output will be different.

That is it for this part of the series. We stop here and continue in the next part.

Chrys

Broad Network

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