PERL has inbuilt data-structures. In this article we will be covering them. In PERL, generically any data structure is called as list. However we can make two broad classification as below :
In this article we will be focusing on Array . In the next article we will be focusing on Associative Array or Hash.
Arrays in PERL :
- In PERL the array is much easier compared to the array in C-Language. Now let us understand how the array is organised in PERL :
- Array/List variables always start with @ (the “at” symbol).
- Arrays/List are variable length.
- Array/List can be declared without length.
- This length can vary even after creation.
- Array/List can contain any sorts of scalars (even a combination of strings, numeric, etc.).
- Array/List elements are written with parentheses.
- Use “my” whenever creating the array/list.
Creation of List/Array in PERL :
We will understand the array creation by code-example as :
The above example is self explanatory .
Accessing an Array/List :
After we have created array , now it is the time to access the array.
- Each array element is accessed as $arr[index]
- my $ref = \@arr ; #gives the reference (pointer) to an array
- my $length = scalar(@arr) ; #gives the array length
- my $LastIndex = $#arr # gives the index of the last element of array
- $arr[-1] #gives the last element of @arr
- Negative indices count backward from the end of an array
- my @arr = (1, 2, 3,4); # four values in the array
- my $ele1 = $arr[0]; # $ele1 gets the 1
- my $ele2 = $arr[1]; # $ele2 gets the 2
- ($arr[0],$arr[1]) = ($arr[1],$arr[0]); # swaps first two elements
The Array of Array :
The array structure can be nested in the below ways :
- my @array1 = (1, 2, 3); #first array
- my @array2 = (4, 5, 6); #second array
- my @array3 = (@array1, @array2); #merged array
- my @list1 = (1, 2, 3); # three values
- my @list2 = @list1; # all three values are copied
- my @list3 = (4, 5, @list2, 6); # six values
Sub-Array or Array Slicing :
A bigger array can be cut/slice in into smaller array in the below way :
- my $arr = qw(apple orange jackfruit grape mango);
- @arr[2,4] # is not a two dimensional array, it is ($a[2], $a[4]);
- my @subArray1 = @arr[2,4] # actually is ("jackfruit" "mango") ;
- my @subArray2 = @arr[2..4] # actually is ("jackfruit" "grape" "mango");
Miscellaneous Array Operations :
Apart from the major operations , we can do some small operation on array as :
- push(@list, $new); # add to end of list. Same as @list = (@list, $new);
- $old = pop(@list); # removes rightmost value
- unshift(@list, $new); # insert at beginning. Same as @list = ($new, @list);
- $old = shift(@list); # removes leftmost value. Same as ($old, @list) = @list;
- @arr = reverse(@arr2); # @arr is the reverse of @arr2
- @arr = sort(@arr2); # sorts on string (ASCII/Alphabetic Order) values
- @sorted = sort { $a <=> $b } @unsorted; # sorts integer/real (ascending Order)
- @sorted = sort { $b <=> $a } @unsorted; # sorts integer/real (descending Order)
- chomp(@arr); # chomps each element of @arr
Array Example :
With the below code , we have exemplified the discussed array operations.
When executed , the above code block gives the below output :
Scalar & List Context in PERL :
Perl has a notion of two different “contexts” in which evaluations can take place:
scalar context and list context.
Things behave differently depending on what context they’re in.
An expression is in “scalar context” if the value it generates will be used as a scalar.
An expression is in “list context” if the value it generates will be used as a list (i.e. an array or hash).
- my @things = (’peach’, 2, ’apple’, 3.1415927);
- my @thing1 = @things;
- my $thing2 = @things;
- my ($thing3) = @things;
- print "\@thing1: @thing1\n";
- print "\$thing2: $thing2\n";
- print "\$thing3: $thing3\n";
my ($first, $second) = @array;
$first and $second are assigned the first and second elements of @array,
my ($first, @rest) = @array;
$first is assigned the first element of @array, and @rest is assigned everything else.
my (@copy, $dummy) = @array;
In this case $dummy is not assigned.
Arrays are variable-length, so @copy has no reason to stop.
Hence $dummy ends up with undef since @copy “eats up” the entire available array.
