Arrays in PHP

An example program that creates and prints an array (output ).
An example program that creates and sorts and prints a single array.(output )
An example program that sorts arrays , and times how long that takes.(output)
Keeping an array around between form executions source (run it here)

Arrays can be indexed by integers ...

• Arrays are accessed with square brackets:
  $names[4] = "Randy";

• Arrays need not contain elements of the same type.  This is legal in PHP, but not in Java/C++
  $names[0] = 1;
  $names[2] = "Two";

• Arrays can be initalized without using an index value.  The default is one above the highest used index.
  $data[] = 0;
  $data[] = 1;
  $data[] = 2;
  $fred[10] = 10;
  $fred[] = 11; // Gets default index 11
  $fred[] = 12; // Gets default index 12

• Arrays can be initialized with the array function
  $countries = array("us", "ca", "mx");

• You can determine the number of elements in the array with the count function:
  $fred[1] = 1;
  $fred[100] = 100;
  $c = count($data); // Returns 2, not 100.  Perl would return 100.

• You can loop through arrays using normal for loops, but this works on arrays with consecutive index values only!
  $c = count($data);
  for($i = 0; $i < $c; $i++) {
      echo($data[$i]);
  }

• You can loop through using a foreach
  foreach ($array as $value) {
  // code
  }
  foreach ($array as $key => $value)
  {

  // code
  }

• You can loop through arrays using the current, key, reset, each, and list functions.  (OLD STYLE BAD, DON'T UNLESS YOU HAVE A REAL NEED)
  This works always:

  • Every array has an element knows as the current element.

  • You can reset the current element to the begining of the array with reset($fred);

  • You can get the index value of the current element with key($fred);

  • You can get the value of the current element with current($fred);

  • You can get the move the current item one further down the array with each.  Each returns both the key and the value of the new current element: list($key, $value) = each($fred);
    You can move one further down the list with next, and one towards the front of the list with prev
    reset($fred);
    echo(next($fred)); // prints 100
    echo(prev($fred)); // prints 1;

Arrays can be indexed with strings

• Everything above still applies

• Use square brackets, not curley ones.
  $countries["ca"] = "canada";

• The array function works really well to assign values, especially with the "=>" operator.
  $countries = array("canada" => "ca", "United States" => us);

Sorting arrays

• Arrays can be sorted with the sort and rsort functions.

• Sorting an array with string indexes moves the value and the index. Don't use sort on arrays with string indexes, or non-consecutive indexes.  The result will be indexes like 0,1,2, ... and not what you want.
  $data["one"] = 1;
  $data[100] = -100;
  sorts to
  $data[0] = -100;
  $data[1] = 1;

• To sort and preserve index values, use asort or arsort.  However, this can result in arrays not in index order for arrays with numbered indexes.
  $data["one"] = 1;
  $data[100] = -100;
  sorts to
  $data[100] = -100;
  $data["one"] = 1;

• To sort by a user defined function, try the usort command (example program) .

• To unsort an array, use shuffle
  shuffle($data);