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Friday, 08 Feb 2008 6:04PM EST

PHP: Multidimentional Arrays

PHP's associative arrays are very powerful in that they allow you to create arbitrary key values, rather than using the simple 0,1,2,3... that most programming languages force on you. For example, if you wanted to create a simple PHP array containing just 2 columns of information, an associative array would be perfect. Take the following 1 dimensional table of data about a pet:

Type	Name	Breed
Dog	Lassie	Collie

To represent this with an associative array:

$pets = array("Type"=>"Dog", "Name"=>"Lassie", "Breed"=>"Collie");

But what if you need to store the following table of data in an array?

Animal	Name	Breed
Dog	Lassie	Collie
Fish	Nemo	Clown Fish
Cat	Garfield	Orange Tabby

You could, of course, create 3 separate arrays; one for each animal. That method is very inefficient, though, and becomes impractical as the table grows. To creat a 2 dimensional array you simply create an array of arrays:

$pets = array( array("Type"=>"Dog", "Name"=>"Lassie", "Breed"=>"Collie"),
               array("Type"=>"Fish", "Name"=>"Nemo", "Breed"=>"Clown Fish"),
               array("Type"=>"Cat", "Name"=>"Garfield", "Breed"=>"Orange Tabby"),
             );

There are two different ways of accessing and displaying the data stored in a 2D array. The first is the manual (and sometimes painful) way:

echo "I have a ".$pets[0]["Type"]." named ".$pets[0]["Name"].". It is a ".$pets[0]["Breed"].".
";
echo "I have a ".$pets[1]["Type"]." named ".$pets[1]["Name"].". It is a ".$pets[1]["Breed"].".
";
echo "I have a ".$pets[2]["Type"]." named ".$pets[2]["Name"].". It is a ".$pets[2]["Breed"].".
";

The second way of accessing the data is to use a for loop (or nested for loops for a non-associative array):

for($i=0; $i<count($pets); $i++) {
  echo "I have a ".$pets[$i]["Type"]." named ".$pets[$i]["Name"].". It is a ".$pets[$i]["Breed"].".
";
}

If we needed to add some more data and further categorize the table, we could just as easily create a 3 dimensional array of data; in this case, organized by animal type:

$pets = array( array( array("Type"=>"Dog", "Name"=>"Lassie", "Breed"=>"Collie"),
                      array("Type"=>"Dog", "Name"=>"Pluto", "Breed"=>"Bloodhound"),
                    ),
               array( array("Type"=>"Fish", "Name"=>"Nemo", "Breed"=>"Clown Fish")
                    ),
               array( array("Type"=>"Cat", "Name"=>"Garfield", "Breed"=>"Orange Tabby"),
                      array("Type"=>"Cat", "Name"=>"Tom", "Breed"=>"Russian Blue")
                    ),
             );

And we could access and display this data with 3 nested for loops (or there's always the manual and painful way):

for($i=0; $i<count($pets); $i++) {
  for($j=0; $j<count($pets[$i]; $i++) {
    echo "I have a ".$pets[$i][$j]["Type"]." named ".$pets[$i][$j]["Name"].". It is a ".$pets[$i][$j]["Breed"].".
";
  }
}

And that's all you need to know to get started using multi-dimensional arrays in PHP. Of course, there are countless variations of this code and uses for it, so take the code, play with it and put it to good use. As always, if you have a technique that you think is better or a tweak that improves on this code, please share it in the comments. If you have a tip, a trick or an idea for my next post, please don't hesitate to contact me.

Friday, 08 Feb 2008 6:04PM EST

PHP: Multidimentional Arrays

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