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What are hashes in Perl?

Samia Ishaque

Hashes in Perl are key value pairs similar to dictionaries in Python. Hash variables can be defined as shown below, similar to how a variable named employees is defined. Each variable is preceded by a sign, and the data is stored within closed brackets (). Each element is separated by ,, but forms pairs of keys corresponding to values.

%employees = ('Samia', 10, 'Ali', 20, 'Sana', 30);

print($employees{'Samia'})

How to define hashes

You can define hash variables as shown below. In the first method, one can simply list a key and its value alternately within () brackets to define the hash variable. Secondly, you can make use of the => arrows to show that one key belongs to another value. Finally, you can also use hyphens (-) to define a key element, but in this case, you must ensure that keys are one-worded.

%employees = ('Samia', 10, 'Ali', 20, 'Sana', 30);
%employeesone = ('Samia' => 10, 'Ali' => 20, 'Sana' => 30);
%employeestwo = (-Samia=> 10, -Ali=> 20, -Sana=>30);

print($employees{'Samia'});
print("\n");
print($employeesone{'Samia'});
print("\n");
print($employeestwo{-Samia});

How to add/remove elements to hashes

You can add or remove elements from hashes as shown below. Adding an element is simple, as you can do so by using the {} brackets; however, deleting requires the use of the special keyword delete. You can observe that Samia has been deleted and Ali has been added.

%employees = ('Samia', 10, 'Sana', 30);

$employees{'Ali'} = 20;
delete $employees{'Samia'};
print "$_ $h{$_}\n" for (keys %employees);

Size of hashes

You can deduce the size of hashes by storing all the keys in one variable and printing that variable’s scalar. helps us put all those keys into scalar context, which means that rather than getting the keys, we acquire the number of keys in a hash or the size of the hash.

%employees = ('Samia', 10, 'Sana', 30);

@allkeys = keys % employees;
$size = @allkeys;
print($size);

Slicing hashes

To slice hashes, you can create arrays of your selected keys using the @ symbol; this slices the hashes into your desired keys.

%employees = ('Samia', 10, 'Sana', 30, 'ali', 20, 'Sania', '40');

@array = @employees{'Samia', 'Sana'};
print(@array);

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