PS_05_Perl - Indexed Arrays (Lists)

Indexed Arrays (Lists)

A list is an ordered set of scalar data. List names follow the same basic rules as for scalars. A reference to a list has the form @foo.

List literals

List literals consist of comma-separated values enclosed in parentheses:

(1,2,3)

(“foo”,4.5)

A range can be represented using a list constructor function (such as “..”):

(1..9) = (1,2,3,4,5,6,7,8,9)

($a..$b) = ($a, $a+1, … , $b-1,$b)

In the case of string values, it can be convenient to use the “quote-word” syntax

@a = (“fred”,”barney”,”betty”,”wilma”);

@a = qw( fred barney betty wilma );

Accessing List Elements

List elements are subscripted by sequential integers, beginning with 0

$foo[5] is the sixth element of @foo

The special variable $#foo provides the index value of the last element of @foo. A subset of elements from a list is called a slice.

@foo[0,1] is the same as ($foo[0],$foo[1])

You can also access slices of list literals:

@foo = (qw( fred barney betty wilma ))[2,3]

List operators and functions

Many list-processing functions operate on the paradigm in which the list is a stack. The highest subscript end of the list is the “top,” and the lowest is the bottom.

push Appends a value to the end of the list

push(@mylist,$newvalue)

pop Removes the last element from the list (and returns it)

pop(@mylist)

shift Removes the first element from the list (and returns it)

shift(@mylist)

unshift Prepends a value to the beginning of the list

unshift(@mylist,$newvalue)

splice Inserts elements into a list at an arbitrary position

splice(@mylist,$offset,$replace,@newlist)

The reverse function reverses the order of the elements of a list

@b = reverse(@a);

The sort function sorts the elements of its argument as strings in ASCII order. You can also customize the sorting algorithm if you want to do something special.

@x = sort(@y);

The chomp function works on lists as well as scalars. When invoked on a list, it removes newlines (record separators) from each element of its argument.