Multidimensional Arrays CIT 336

The Basics Explaining Multidimensional Arrays

Arrays An array is a serial collection of data. In most programming languages, including PHP, individual array elements are accessed using the following syntax: variableName[index] Ex: $boolArr[2] = true; In the example above, the 3 rd item in the $boolArr array is being accessed (indexes are 0-based, so the first item is accessed at index: 0, the second item at index: 1, and so on.) $boolArr [0]: true [1]: false [2]: true [3]: true

2D Arrays A ‘normal’ array is one dimensional, meaning it has elements ranging from index:0 to index:n. However, arrays do not necessarily need to be limited to one dimension. We could represent a 2D array by using two indexers like this: variableName[index1][index2] Ex: $intArr2D[1][2] = 2; Notice, there are now two indexers, giving our array two dimensionality. The next slide demonstrates this using a table to illustrate. This concept can be expanded to any number of dimensions, for example, a three dimensional array would be accessed like this: $doubleArr3D[0][9][6] = 3.4f; $intArr2D [0][0]: 0 [0][1]: 0 [0][2]: 0 [1][0]: 0 [1][1]: 1 [1][2]: 2 [2][0]: 0 [2][1]: 2 [2][2]: 4

2D Array - Rectangular $intArr2D[0][?][1][?][2][?] [?][0][0][0]: 0[1][0]: 0[2][0]: 0 [?][1][0][1]: 0[1][1]: 1[2][1]: 2 [?][2][0][2]: 0[1][2]: 2[2][2]: 4 This is an example of a “rectangular” array – an array of arrays where the nested arrays are all the same size (in this case, each nested array contains 3 elements).

Jagged Arrays Another type of multidimensional array is a Jagged Array. A jagged array is also an array of arrays, but in this case, the nested arrays may each be of different lengths. Consider the example to the right – $jagged[0] contains 3 elements, but $jagged[1] only contains 2 elements, while $jagged[2] contains 5 elements. This variation in nested element length is why the this sort of array is called a Jagged Array. $jagged[0] [0]: ' a ' [1]: ' b ' [2]: ' c ' $jagged[1] [0]: ' 1 ' [1]: ' 2 ' $jagged[2] [0]: '. ' [1]: ', ' [2]: ' ; ' [3]: ' ! ' [4]: ' ? '

2D Array - Jagged $jagged[0][?][1][?][2][?] [0][0]: 'a'[1][0]: '1'[2][0]: '.' [0][1]: 'b'[1][1]: '2'[2][1]: ',' [0][2]: 'c'[2][2]: ';' [2][3]: '!' [2][4]: '?' This is an example of a “jagged” array – an array of arrays where the nested arrays can be of varying sizes.

Creating & Accessing Multidimensional Arrays The process for creating a multidimensional array is very similar to the process for creating a single dimensional array. Essentially, a “normal” array is first created, and then arrays are created and assigned as elements of that array. For example: $myArray = array(); $myArray[0] = array(); $myArray[1] = array();... $myArray[99] = array(); This demonstrates manually assigning each nested array, but a for loop could certainly be used. Elements of multidimensional arrays are accessed just like one dimensional arrays, only additional indexers are used. $board[0][0] = false; $cell[15][6] = 16.4; $names[3]['first'] = 'Don';

Application Using Multidimensional Arrays

When do we use them…? There are a number of cases where multidimensional arrays are the natural choice for a data structure. For instance, in the case of modeling a chess board, a two dimensional array makes a lot of sense; a chess board is really a 2D array of squares and representing it with a 2D array of variables is pretty straightforward. Tabular data may also be a good candidate for using a 2D array. Tables also make easy transitions to 2D arrays because they themselves our laid out in a similar fashion (rows by cols) and are easy to translate into array[row][col] structure.

Practical Example An example from our textbook that doesn’t model a typical 2D object is an online shopping cart. The shopping cart is represented as an array. In this case, it will be an array of items (themselves an array), creating a multidimensional array. $shoppingCart = array(); Then, each item is represented as an associative array. $item = array(); $item['product_name'] = 'Book'; $item['product_price'] = 15.05; $item['item_quantity'] = 1; Items are then "added to the cart" simply by adding them to the $shoppingCart array. $shoppingCart[] = $item; Additional items can easily be defined and added. The $shoppingCart array contains a series of items, and each item contains its own set of elements. This same approach can be used could be used to represent employees within a department, departments within an organization, and even organizations within groups of organizations.