PHP Arrays

Jussi Pohjolainen

Tampere Polytechnic University of Applied Sciences » ICT

Intro to php arrays

• PHP arrays are not arrays. :) They are infact a data structure called ordered map
• Map (or associative array) is a type that maps values to keys.
• So instead of using normal array indexes (0..n), you use keys.
• Array type can be used for several data structures: List, Hashtable, dictionary, collection, stack and queue.

Intro to php arrays

• PHP arrays have an internal order to their elements that is independent of the keys and values.
• It's possible to go through values on this internal order
• Order is normally that in which values were inserted into the array

Creating a Array

• Array can be created using array() function.
• Creating associative array with keys and values:

  • $phonebook = array ("Jack Bauer"     => 98723489,
                        "Vesa Keskinen"  => 1234567);
    

• You can also create a array by setting values in it
• Example: $test[0] = 12; $test['x'] = "hi!";
• Printing the values: print $test['x'];

Declaring keys

• It is not always mandatory to declare a key. If key is not specified, it is created for you.
• Setting initial key:

  • $colors = array(1 => 'Black', 'Blue', 'Yellow');
    =>
    $colors = array(1 => 'Black', 2 => 'Blue', 3 => 'Yellow');
    

• If no initial key is given:

  • $colors = array('Black', 'Blue', 'Yellow');
    =>
    $colors = array(0 => 'Black', 1 => 'Blue', 2 => 'Yellow');
    

Keys

• Array key can be either an integer or a string.
• If string key is a representation of an integer, it will be cast typed to integer: "12" => 12
• Float values are truncated to integer
• Value true is transformed to integer 1 and value false to 0
• Example

  $test = array(  "2" => "are",
                  3.4 => "you?",
                 true => "how",
                false => "Hi,");
  

• What are the keys?

Adding values to the end of an array

• Easiest way to add values to an indexed array is to use [] syntax:

• $students = array("Jack", "Bill");
  $students[] = "Lisa";
  

• This creates key-value pair 2 => "Lisa"
• If the array is not indexed, PHP puts the new value to key 0

Getting the size of an array

• There are functions to get the array's size: count() and sizeof() (indentical)
• Returns the number of elements in the array
• Example

  $colors = array('white', 'blue');
  $size = count($colors);
  

Traversing arrays: foreach

• There are several ways to traverse arrays: Foreach, iterators, for and array_walk
• Most common way to loop over elements: foreach:

  $colors = array('black', 'blue', 'red');
  foreach ($colors as $color) {
      print $color;
  }
  

• And the result is blackbluered
• Alternative form of foreach:

  $persons = array('Jack Bauer' => 98723489);
  foreach ($persons as $name => $number) {
      print "$name, $number";
  }
  

Traversing arrays: for

• If the array is indexed array, it's possible to use for-loop.
• Printing array values using for:

  $colors = array('black', 'blue', 'red');
  for($i=0; $i < count($colors); $i++) {
      print $colors[$i];
  }
  

Searching values

• The in_array() function can be used for searching values in an array.
• Returns boolean value
• Example:

  $colors = array('black', 'blue', 'red');
  if(in_array('black', $colors) {
      ...
  }
  

• The array_search() function returns the key of the found element.

Multidimensional Arrays

• Values in an array can themselves be arrays => multidimensional array

• $row0 = array(1,2,3);
  $row1 = array(4,5,6);
  $row2 = array(7,8,9);
  $multidimensional = array($row0, $row1, $row2);
  

• Referring to a value: print $multidimensional[0][1];

Other useful functions

• sort(), asort(), ksort()
• array_reverse(), array_flip()
• shuffle()
• array_sum(), array_merge()