Passing arrays by value and reference

The difference between passing by value and passing by reference is that you when pass by value, you are passing a copy of the array. When passing by reference, you are passing a pointer i.e any changes made in the function you pass to can modify the original.

function foo($var) {
  $var[1]++;
}
function bar(&$var) {
  $var[1]++;
}

$a=array(5,6,7);
foo($a);
print "Passed by value:\n";
print_r($a);
bar($a);
print "Passed by reference:\n";
print_r($a);

output

Passed by value:
Array
(
  [0] => 5
  [1] => 6
  [2] => 7
)
Passed by reference:
Array
(
  [0] => 5
  [1] => 7
  [2] => 7
)

When passed by value, elements of $a remain unchanged. When passed by reference, the second element of $a changed. The only difference in code is the & in the function parameter.

Removing duplicates values from an array

The array_unique function removes duplicates from an array.

$aSample = array(1,1,6,6,6,8,"8");
print_r(array_unique($aSample));

output

Array ( [0] => 1 [2] => 6 [5] => 8 )

By default all values are compared as strings, thus there is no difference between 8 and "8".

print_r into a variable

print_r() prints array contents in a user-friendly format. The output of print_r() can also be stored into a variable. Just remember to pass your array into print_r() with a true flag as follows:

$a = array('pass','print_r','into','variable');
$variable = print_r($a,true);
print $variable;

output

Array
(
  [0] => pass
  [1] => print_r
  [2] => into
  [3] => variable
)

Removing a element from an array

To remove an element from an array, we use array_splice().

$arr = array("red", "green", "blue", "black");
print_r($arr);
for ($i = 0; $i < count($arr); $i++) {
  if ($i == 2) {
  array_splice($arr, $i, 1);
  }
}
print_r($arr);

The element blue has been removed from the array.

Array
(
  [0] => red
  [1] => green
  [2] => blue
  [3] => black
)
Array
(
  [0] => red
  [1] => green
  [2] => black
)

Push and Pop

array_push() and array_pop() functions are used to push and pop elements on a array. These functions have the following syntax:

array_push($array,$element);
$element = array_pop($array);

Lets look at the following code:

$mya = array(0 => "zero",1 => "one",2 => "two");
array_push($mya, "three");
$mya[] = "four";
print_r($mya);

This program would produce the following results. array_push() adds an element at the end of the array. The code on the last line is equivalent to a pop.

Array
(
  [0] => zero
  [1] => one
  [2] => two
  [3] => three
  [4] => four
)

array_pop removes the last element from an array. Let's look at the following program:

$mya = array(0 => "zero",1 => "one",2 => "two");
$n = array_pop($mya);
print "$n\n";
print_r($mya);

This program produces the following result.

two
Array
(
  [0] => zero
  [1] => one
)