PHP: Multidimensional Arrays II

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Multidimensional Arrays II

Aims:

• to understand the difference between rectangular 2-dimensional arrays and ragged 2-dimensional arrays
• to practice writing programs for both rectangular and ragged 2-dimensional arrays

Class exercise

• A relief map, showing height above mean sea level (in metres), for a 100 square metre area of Outer Nerdland can be represented by a 100 × 100 2-dimensional array
• E.g. this can be represented as an array called $map:

  100	100	103	104	103	100	100	103	104	103	...
  100	100	105	104	103	108	99	98	97	96	...
  100	101	104	104	103	106	100	99	98	97	...
  100	100	103	103	102	105	104	103	102	101	...
  ...	...	...	...	...	...	...	...	...	...	...

• A peak is a cell that is higher than all of its immediate neighbouring cells to the north, east, south and west
• Write a PHP script that counts the number of peaks in $map
• Hint: use for-loops, not foreach-loops

Rectangular arrays

• The multidimensional arrays we have seen so far are sometimes called rectangular: the 'inner' arrays are all of the same length

Ragged arrays

• However, there is nothing to prevent the 'inner' arrays from being of different lengths
• In this case, the multidimensional arrays are sometimes called ragged
• E.g. Donna Kebab is studying Witchcraft at the National University of Nerdland, where some modules have more pieces of coursework than others:

  $donnas_grades = array
      (
          'WC1101' => array(85,  0,  0,  0),
          'WC1102' => array(72, 75, 91, 60, 34, 35),        
          'WC1103' => array(57, 57, 57, 57, 57)
      );

Class exercises

1. Write a PHP script that outputs Donna's grades as nested unordered lists, as follows:
   • WC1101
     • 85
     • 0
     • …
   • WC1102
     • …
   • …
2. Write a PHP script that outputs Donna's grades as a table. Make all rows in the table the same length by 'padding' them with cells that contains hyphens (<td>-</td>), as follows:

   WC1101	85	0	0	0	-	-
   WC1102	72	75	91	60	34	35
   WC1103	57	57	57	57	57	-