Arrays are also a big part of the Perl language and Perl has a lot of functions to help you work with them. Some of the actions arrays perform include deleting elements, checking for the existence of an element, reversing all of the the elements in an array, and sorting the elements.
Here are the functions you can use with arrays:
As with the string functions, only a few of these functions will be explored.
Example: Printing an Associative Array
The each() function returns key, value pairs of an associative array one-by-one in a list. This is called iterating over the elements of the array. Iteration is a synonym for looping. So, you also could say that the each() function starts at the beginning of an array and loops through each element until the end of the array is reached. This ability lets you work with key, value pairs in a quick easy manner.
The each() function does not loop by itself. It needs a little help from some Perl control statements. For this example, we'll use the while loop to print an associative array. The while (CONDITION) {} control statement continues to execute any program code surrounded by the curly braces until the CONDITION turns false, assoc.pl.
%array = ( "100", "Green", "200", "Orange");
while (($key, $value) = each(%array)) {
print("$key = $value\n");
}
This program prints:
100 = Green 200 = Orange
The each() function returns false when the end of the array is reached. Therefore, you can use it as the basis of the while's condition. When the end of the array is reached, the program continues execution after the closing curly brace. In this example, the program simply ends.
Example: Checking the Existence of an Element
You can use the defined() function to check if an array element exists before you assign a value to it. This ability is very handy if you are reading values from a disk file and don't want to overlay values already in memory. For instance, suppose you have a disk file of Jazz Artist addresses and you would like to know if any of them are duplicates. You check for duplicates by reading the information one address at a time and assigning the address to an associative array using the Jazz Artist name as the key value. If the Jazz Artist name already exists as a key value, then that address should be flagged for follow up.
Because we haven't talked about disk files yet, we'll need to emulate a disk file with an associative array. And, instead of using Jazz Artist's address, we'll use Jazz Artist number and Jazz Artist name pairs. First, we see what happens when an associative array is created and two values have the same keys, element1.pl.
createPair("100", "Miles Davis");
createPair("200", "Keith Jarrett");
createPair("100", "John Coltrane");
while (($key, $value) = each %array) {
print("$key, $value\n");
};
sub createPair{
my($key, $value) = @_ ;
$array{$key} = $value;
};
This program prints:
100, John Coltrane 200, Keith Jarrett
This example takes advantages of the global nature of variables. Even though the %array element is set in the createPair() function, the array is still accessible by the main program. Notice that the first key, value pair (100 and Miles Davis) are overwritten when the third key, value pair is encountered. You can see that it is a good idea to be able to determine when an associative array element is already defined so that duplicate entries can be handled. The next program does this, element2.pl.
createPair("100", "Miles Davis");
createPair("200", "Keith Jarrett");
createPair("100", "John Coltrane");
while (($key, $value) = each %array) {
print("$key, $value\n");
};
sub createPair{
my($key, $value) = @_ ;
while (defined($array{$key})) {
$key++;
}
$array{$key} = $value;
};
This program prints:
100, Miles Davis 101, John Coltrane 200, Keith Jarrett
You can see that the number for John Coltrane has been changed to 101.