1. Introduction to PHP – Part 2 Sudeshna Dey

2. Arrays A series of homogeneous elements Elements have values in form of stored data Has a key associated with every element – Values get associated to keys – Arrays specified as key-value pairs Effectively an ordered map

3. Arrays (cont’d) Initialization can be done in different ways Ex: array( key => value, key2 => value2, key3 => value3,... ) – Comma after the last element is optional and may not be used The key is usually an Integer or a String The value can be of any data type

4. Arrays (cont’d) // On earlier versions “value1", “key2" => “value2", ); // PHP 5.4 onwards $array = [ “key1" => “value1", “key2" => “value2", ]; ?>

5. Arrays (cont’d) If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten Input – “x", 1.7 => “y", "1" => “z" ); ?> Output – array(1) { [1]=> string(1) “z" }

6. Arrays (cont’d) Useful in passing messages across webpages – Used to pass around session variables using named keys If no index is specified, then the default indexing starts at 0 (integer) and then counts upwards as one keeps adding elements to the array

7. Arrays (cont’d) $first = array(); $first[‘size'] = ‘big'; $first[‘shape'] = ‘cubic'; $first[‘density'] = ‘high'; $first[‘type'] = ‘compound'; $first[] = 100; // $first[0]=100; $second = array(); $second[] = ‘x'; $second[] = ‘y'; $second[] = ‘z'; // Result of the above: // $first = array('size' => 'big', 'shape' => 'cubic', 'density' => 'high ', 'type' => 'compound', '0' => 100) // $second = array(0 => 'x‘, 1 => 'y', 2 => 'z')

8. Array (cont’d) $value) { unset($array[$i]); } print_r($array); // Append an item (note that the new key is 5, instead of 0). $array[] = 6; print_r($array); // Re-index: $array = array_values($array); $array[] = 7; print_r($array); ?>

9. Array (cont’d) By default, arrays are 0-index based But, one can set 1-index based arrays 'January', 'February', 'March'); print_r($firstquarter); ?> Output array ( [1] => 'January' [2] => 'February' [3] => 'March' )

10. Array (cont’d) Arrays can be sorted with inbuilt commands

11. Array (cont’d) Arrays can have any content inside them – Hence, arrays can contain arrays – This leads to creation of multidimensional and recursive arrays array ( "a" => "orange", "b" => "banana", "c" => "apple"),"numbers" => array ( 1, 2, 3, 4, 5, 6), "holes" => array ( "first", 5 => "second", "third")); // Some examples to address values in the array above echo $fruits["holes"][5]; // prints "second" echo $fruits["fruits"]["a"]; // prints "orange" unset($fruits["holes"][0]); // remove "first" // Create a new multi-dimensional array $juices["apple"]["green"] = "good"; ?>

12. Array (cont’d) Array assignment involves copying one array into the other Involves value-copying –

13. Array (cont’d) The array_diff() function compares array values two or more arrays – Returns an array with the keys and values from the first array, only if the value is not present in any of the other arrays – Only the value is used for the comparison, not the key – "Cat",1=>"Dog",2=>"Horse"); $a2=array(3=>"Horse",4=>"Dog",5=>"Fish"); print_r(array_diff($a1,$a2)); ?> – Output: Array ( [0] => Cat ) General syntax: array_diff(array1,array2,array3...)

14. Array (cont’d) The array_diff_assoc() function compares two or more arrays – Returns an array with the keys and values from the first array, only if they are not present in any of the other arrays – Uses both the keys and the values for comparison – "Cat",1=>"Dog",2=>"Horse"); $a2=array(0=>"Rat",1=>"Horse",2=>"Dog"); $a3=array(0=>"Horse",1=>"Dog",2=>"Cat"); print_r(array_diff_assoc($a1,$a2,$a3)); ?> – Output: Array ( [0] => Cat [2] => Horse ) General syntax: array_diff_assoc(array1,array2,array3...)

15. Array (cont’d) The array_combine() function creates an array by combining two other arrays – The first array is the keys – The second array is the values General syntax: array_combine(array1,array2) Output: Array ( [a] => Cat [b] => Dog [c] => Horse [d] => Cow )

16. Array (cont’d) The array_filter() function passes each value in the array to a user-made function – The user-made function returns either true or false – The array_filter() returns an array only with the values that returned true – "Dog",1=>"Cat",2=>"Horse"); print_r(array_filter($a,"myfunction")); ?> – Output: Array ( [2] => Horse )

17. Array (cont’d) The array_intersect() function compares two or more arrays – Returns an array with the keys and values from the first array, only if the value is present in all of the other arrays – "Cat",1=>"Dog",2=>"Horse"); $a2=array(3=>"Horse",4=>"Dog",5=>"Fish"); print_r(array_intersect($a1,$a2)); ?> – Output: Array ( [1] => Dog [2] => Horse )

18. Array (cont’d) The array_key_exists() function checks an array for a specified key – Returns true if the key exists – Returns false if the key does not exist – "Dog","b"=>"Cat"); if (array_key_exists("a",$a)) { echo "Key exists!"; } else { echo "Key does not exist!"; } ?> – Output: Key exists!

19. Array (cont’d) The array_merge() function merges one or more arrays into one array – "Horse","b"=>"Dog"); $a2=array("c"=>"Cow","b"=>"Cat"); print_r(array_merge($a1,$a2)); ?> – Output: Array ( [a] => Horse [b] => Cat [c] => Cow ) Can use array_merge() with only one parameter

20. Array (cont’d) The array_merge_recursive() function merges one ore more arrays into one array The difference between this function and the array_merge() function is when two or more array elements have the same key, instead of override the keys, the array_merge_recursivse() function makes the value as an array Sample code: – "Horse","b"=>"Dog"); $a2=array("c"=>"Cow","b"=>"Cat"); print_r(array_merge_recursive($a1,$a2)); ?> – Output: Array ( [a] => Horse [b] => Array ( [0] => Dog [1] => Cat ) [c] => Cow )

21. Array (cont’d) The array_pop() function deletes the last element of an array – – Output: Array ( [0] => Dog [1] => Cat ) – General syntax: array_pop(array)

22. Array (cont’d) The array_reverse() function returns an array in the reverse order – "Dog","b"=>"Cat","c"=>"Horse"); print_r(array_reverse($a)); ?> – Output: Array ( [c] => Horse [b] => Cat [a] => Dog )

23. Array (cont’d) The array_shift() function removes the first element from an array – Returns the value of the removed element – "Dog","b"=>"Cat","c"=>"Horse"); echo array_shift($a); print_r ($a); ?> – Output: Dog Array ( [b] => Cat [c] => Horse ) – If the keys are numeric, all elements will get new keys, starting from 0 and increases by 1 – "Dog",1=>"Cat",2=>"Horse"); echo array_shift($a); print_r ($a); ?> – Output: Dog Array ( [0] => Cat [1] => Horse )

24. Array (cont’d) The array_walk() function runs each array element in a user-made function – The array's keys and values are parameters in the function – Returns True or False – "; } $a=array("a"=>"Cat","b"=>"Dog","c"=>"Horse"); array_walk($a,"myfunction"); ?> – Output: The key a has the value Cat The key b has the value Dog The key c has the value Horse

25. Array (cont’d) The asort() function sorts an array by the values – Values keep their original keys – Returns TRUE on success, or FALSE on failure – "Dog", "b" => "Cat", "c" => "Horse"); asort($my_array); print_r($my_array); ?> – Output: Array ( [b] => Cat [a] => Dog [c] => Horse )

26. Array (cont’d) The arsort() function sorts an array by the values in reverse order – Values keep their original keys. – Returns TRUE on success, or FALSE on failure – "Dog", "b" => "Cat", "c" => "Horse"); arsort($my_array); print_r($my_array); ?> – Output: Array ( [c] => Horse [a] => Dog [b] => Cat )

27. Array (cont’d) The array_values() function returns an array containing all the values of an array – "Cat","b"=>"Dog","c"=>"Horse"); print_r(array_values($a)); ?> – Output: Array ( [0] => Cat [1] => Dog [2] => Horse )

28. Array (cont’d) The array_sum() function returns the sum of all the values in the array – "5",1=>"15",2=>"25"); echo array_sum($a); ?> – Output: 45

29. Array (cont’d) The explode() function breaks a string into an array – General syntax: explode(separator,string,limit) – – Output: Array ( [0] => Hello [1] => world. [2] => It's [3] => a [4] => beautiful [5] => day. )

30. Array (cont’d) The implode() function returns a string from the elements of an array – General syntax: implode(separator,array) The separator parameter is optional these days, but recommended to use for backward compatibility – – Output: Hello World! Beautiful Day!