perl-data types | intophysicaldesign

Data Types

Scalars ($)

Definition: Scalars are single data items, which can be a number, a string, or a reference.
In Perl, scalars are prefixed with a dollar sign ($).
Usage: Scalars are used to store individual pieces of data like numbers, text, or Boolean values.
Example:

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my $name = "Alice";    # String scalar
my $age = 30;          # Numeric scalar
my $height = 5.8;      # Floating-point scalar
my $is_active = 1;     # Boolean scalar (1 for true, 0 for false)

Perl allows different operations on scalars, including mathematical operations for numbers and concatenation for strings

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my $sum = $age + 10;              # 40
my $greeting = "Hello, " . $name; # String Concatenation -> "Hello, Alice"

Example:

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my $a = 10;
print "value of a is $a\n";

my $result = "this is \"number\"";
print "$result, hello\n";
print "\$result, $a\n";

Output of the above code:

value of a is 10
this is "number", hello
$result, 10

2. Arrays (@)

Definition: Arrays are ordered lists of scalars.
Each element in an array can be accessed using its index, starting from 0.
In Perl, arrays are prefixed with an at symbol (@).
Usage: Arrays are useful for storing a list of items, like a collection of names, numbers, or other scalar values.
Example:

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my @colors = ("red", "blue", "green"); # Array of strings
my @numbers = (1, 2, 3, 4, 5);         # Array of numbers

Accessing Array Elements:

To access individual elements -> $array[ ]

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my @colors = ("red", "blue", "green"); # Array of strings
print $colors[0];

Output of the above code:

red

Example:

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my @array = ("a","b","c","1","2","hello","hello world");

print "@array\n";           		#output: a b c 1 2 hello hello world
print @array,"\n";         		#output: abc12hellohello world 

print "$array[5]\n";        		#output: hello
print "@array[2,5]\n";      		#output: c hello
print "@array[3..5]\n";     		#output: 1 2 hello

#Negative index is also possible,starts from -1
print "$array[-6]\n";       		#output: b
print "@array[-2,-5]\n";    		#output: hello c
print "@array[-5..-2]\n";   		#output: c 1 2 hello

We can replace the space character between the output elements of an array with another character by using '$" .

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my @array = ("a","b","c","d","e");
$" = "xx";

print "@array\n";

Output of the above code:

axxbxxcxxdxxe

Size of an array (or) No. of elements in an array:

Storing an array into a scalar variable will give us the size of an array.

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my @abc = ("a".."z");              # range operator(..)
my $size = @abc;

print "@abc\n";
print "$size\n";

Output of the above code:

a b c d e f g h i j k l m n o p q r s t u v w x y z
26 ----> size of array @abc

using 'scalar' function to know size of array

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my @abc = ("a".."z");
print scalar@abc,"\n";		#output: 26

Last index of an array:

$#array_name gives the index of the last element in the array.
Since Perl arrays are zero-indexed, the last index will be the total number of elements minus one.

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my @numbers = (10, 20, 30, 40, 50); 
my $last_index = $#numbers;         
print "Last index: $last_index\n";  

# or simply, print "$#numbers\n";

Output of the above code:

Last index: 4

If the array is empty, $#array_name will return -1, indicating that there are no elements.

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my @empty_array = ();
print "Last index: ", $#empty_array, "\n";  # Output: Last index: -1

You can use $#array_name to access the last element of the array:

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my @numbers = (10, 20, 30, 40, 50); 
print "Last element: $numbers[$#numbers]\n"; 		#Output: Last element: 50

Inserting new elements into an array

You can assign a value directly to a specific index in the array.
If the index is beyond the current size of the array, Perl will automatically extend the array and fill the intervening spaces with undef.

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my @fruits = ("apple", "banana");
$fruits[2] = "cherry";            
print "@fruits\n";                # Output: apple banana cherry

$fruits[5] = "date";             
print "@fruits\n";                # Output: apple banana cherry undef undef date

There are other functions to insert new elements into an array like 'push', 'unshift', 'splice' which will be discussed later.

Merging of arrays

You can combine two arrays using the array concatenation operator (push or direct assignment).
Using direct assignment:

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my @array1 = (1, 2);
my @array2 = (3, 4);
my @merged = (@array1, @array2);  
print "@merged\n";                     # Output: 1 2 3 4

using 'push' :

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my @array1 = (1, 2);
my @array2 = (3, 4);
push @array1, @array2;            # Add all elements of @array2 to @array1
print "@array1\n";                # Output: 1 2 3 4

Examples:

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my @numbers = (1, 2, 3, (4, 5, 6), 7, 8, 9);

print "@numbers\n";			#Output: 1 2 3 4 5 6 7 8 9
print "$numbers[3]\n";			#Output: 4
print "@numbers[3..8]\n";		#Output: 4 5 6 7 8 9

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my @numbers = (1, 2, 3, (4, 5, 6), 7, 8, 9);

print "@numbers\n";		                	#Output: 1 2 3 4 5 6 7 8 9
print "$numbers[$#numbers-2]\n";			#Output: 7
print "@numbers[$#numbers-2..$#numbers]\n";		#Output: 7 8 9

3. Hash (%)

Definition: a hash is an unordered collection of key-value pairs where each key is associated with a corresponding value.
Keys in a hash must be unique, but values can be duplicated.
NOTE: keys are case sensitive.
Values can be any scalar data types.

Declaring a Hash

To declare a hash, use the % symbol followed by the hash name.

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my %hash_name = (key1 => value1, key2 => value2, key3 => value3);

Accessing hash elements

You can access a value by specifying its key inside curly braces { } and prefixing the hash name with $.
Example:

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

print "$data{'AND'}\n";         #NOTE: Key name should be enclosed in single quotes only or no quotes at all
print "$data{'NOR'}\n";
print "$data{'NAND'}\n";

Output of the above code:

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45
30
hello world

We can access multiple multiple elements by storing them into an array
Example:

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

my @array = @data{'AND','NOR'};

print "@array\n";           #Output: 45 30

Adding or Modifying Elements

You can add a new key-value pair or modify an existing one by assigning a value to a key.

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

$data{'XOR'} = 100;      #Add new key-value pair 
$data{'NOR'} = 26;       #Update value for the key 'NOR'

Deleting elements

Use the delete function to remove a key-value pair from a hash.

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delete $data{'NAND'}

Check existance of a key

Use the exixst function to check wether a key exists or not in a hash

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print exists $data{'NAND'};

Printing keys only

Use the 'keys %hash' function and store them into an array, then print the array

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

my @array = keys %data;

print "@array\n";	#Output: NOR AND NAND (unordered)

Printing values only

Using the 'values %hash' function.

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my @array = values %data;

print "@array\n";	#Output: 30 45 hello world (unordered)

Size of a hash

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my %data = (AND => 45, NOR => 30, NAND => "hello world");
my @array = keys %data;		#or values %data

print "the size of hash is",scalar @array,"\n";

Output of the above code:

the size of hash is 3

Miscellaneous

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

print %data,"\n";       #Output: NOR30AND45NANDhello world
print "%data\n";	#Output: %data
print "@data\n";	#prints nothing
print "$data\n";	#prints nothing

Storing hash into array

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

my @array_data = %data;

print "%data\n";	
print "@array_data\n";

Output of the above code:

%data
NOR 30 AND 45 NAND hello world

Printing a hash

Using each function and while loop

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

while (my ($key, $value) = each %data) {
    print "$key => $value\n";
}

Output of the above code:

AND => 45
NOR => 30
NAND => hello world

Another way, Using keys and values

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my %data = (AND => 45, NOR => 30, NAND => "hello world");

foreach my $key (keys %data) {
    print "$key => $data{$key}\n";
}

Data Types

Scalars ($)

2. Arrays (@)

Accessing Array Elements:

Size of an array (or) No. of elements in an array:

Last index of an array:

Inserting new elements into an array

Merging of arrays

3. Hash (%)

Declaring a Hash

Accessing hash elements

Adding or Modifying Elements

Deleting elements

Check existance of a key

Printing keys only

Printing values only

Size of a hash

Miscellaneous

Storing hash into array

Printing a hash