Array Basics

We've looked at arrays and some of the basic array operators in a

previous article (back in March 2000), so in this article we'll revisit

arrays from a slightly different angle -- when and how to use them.

Often I see cases where a list of data is assigned to an equal list of

scalar variables, as in the following hypothetical database-

reformatting task:

#!/usr/bin/perl -w

use strict;

while(<>){

chomp;

my ($id, $lname, $fname, $department,

$location, $shift) = split /:/;

print "$lname|$fname|$id|$shift|$department|$location\n";

}

__END__

Assigning each field to a named scalar can be beneficial when reusing

many of them variously throughout the rest of the block (self

documenting code); however, the above usage is trivial and unnecessary.

If we are merely reformatting the data, or perhaps storing it in a

larger data structure for later use, we do not need to create all of

these variables:

#!/usr/bin/perl -w

use strict;

while(<>){

chomp;

my @fields = split /:/;

print join('|', @fields[1,2,0,5,3,4]),"\n";

}

__END__

In this case, we are just reformatting the data. Rather than specify

each field name in the new ordering, we need only re-join the fields in

their new order using an array slice.

Another good place to use an array is in building a hash. That's right,

we can easily use an array as a list of keys when building a hash by

using a hash-slice. Consider reading in the same type of data above but

this time we wish to build a hash using field names for keys:

#!/usr/bin/perl -w

use strict;

my @fields = qw/id lname fname department location shift/;

while(<>){

chomp;

my %data;

@data{@fields} = split /:/;

process(\%data); # do something with %data hash

}

# process subroutine definition ...

__END__

Besides being easy to follow, the above method allows you to eventually

process the data fields in the order they occur. You can loop through

the array of keys rather than using the keys() function (which does not

return keys in the order they were entered in the hash). An advantage

to be sure.

As a final array example, let

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