Molemen...From the Second Dimension! - Perl

Welcome to the ninth installment in our look at working with hashes and lists in Perl. In our previous article we learned how to add records to a hash, replace them, and delete the values inside of them. In this article we will learn how to check whether records reside within our hashes, write the data within a hash to a file, and create multidimensional lists.

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By: James Payne

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May 12, 2008

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Two-dimensional lists are lists that have other lists as their items. Go ahead. Grab that mop and clean up the mess I just made by making your head explode. In the next few examples, we are going to pretend that we have a database of lame superheroes that just never made it. Each record will consist of the following:

Secret Lair
Name
Super power
Super weakness

Let's go ahead and create our first two-dimensional array:

#!/usr/bin/perl

@StuporHeroes = (

[' Mount Tittikanaka ', ' Man-Girl ', ' Is a good listener ', ' Has

Man-Boobs '],

['Trailer Park', 'Deaf Leapard', 'Has a super sonic guitar', 'Is deaf

and has one arm making him unable to play his guitar']

);

In the above example, we created a two-dimensional list named @StuporHeroes. You will note that even though our list has an added dimension, we still use the @ symbol before the name, just as with our normal lists. We then encase the values in our two-dimensional list with square brackets, instead of parentheses as per normal lists. Each piece of data or “cell” is separated by a comma. Each row of data is placed between a set of parentheses, ending in a semi-colon, as shown above.

If this seems a little confusing at the moment, that is all right. When I explain them in the next section everything will become crystal clear.

Better Understanding the Two-Dimensional List

The best way to think of a two-dimensional list is to imagine an Excel sheet. I used that same analogy with hashes, but really it applies more to this storage device. For instance, in a spreadsheet you enter data into a grid, like the one shown below:

As you can see, the value Spiderman is located at row 3, column A. Batman is row 5, column A, Thanos is row 8, column B, and so forth. This is how Perl sees your record. In our sample code above for instance, we assigned our lists values like this:

@StuporHeroes = (

[' Mount Tittikanaka ', ' Man-Girl ', ' Is a good listener ', ' Has

Man-Boobs '],

['Trailer Park', 'Deaf Leapard', 'Has a super sonic guitar', 'Is deaf

and has one arm making him unable to play his guitar']

);

Our first row contains all of the following data: “Mount Tittikanaka”, “Man-Girl”, “Is a good listener” and “Has man boobs”. Note that with lists, element numbers start at 0. All of these elements have a row number of zero. However there column number differs. If I wanted to call on “Mount Tittikanaka” for instance, I would search for the value in row 0, column 0. If I wanted “Man-Girl”, I would search in row 0, column 1, and so forth.

The second row contains the values: “Trailer Park”, “Deaf Leapard”, “Has a super sonic guitar”, and “Is deaf and has one arm making him unable to play his guitar”. If I wanted to refer to “Trailer Park” I would point to row 1, column 0. “Deaf Leopard” is located at row 1 and column 1. Always keep in mind that elements start at 0 (as do our rows and columns).

Well that's it for this article. In our next episode we will learn to print from our extra-dimensional lists, and figure out other ways to manipulate the data contained within them. So be sure to stop back often!

Till then...