Filter array - odd even

Question

How can a filter out the array entries with an odd or even index number?

Array
(
    [0] => string1
    [1] => string2
    [2] => string3
    [3] =&         


        

Answer 1

I'd do it like this...

for($i = 0; $i < count($array); $i++)
{
    if($i % 2) // OR if(!($i % 2))
    {
        unset($array[$i]);
    }
}

Answer 2

<?php 
$array = array(0, 3, 5, 7, 20, 10, 99,21, 14, 23, 46); 
for ($i = 0; $i < count($array); $i++) 

{ 
        if ($array[$i]%2 !=0)
        echo $array[$i]."<br>";
}
?> 

Answer 3

Here's a "hax" solution:

Use array_filter in combination with an "isodd" function.

array_filter seems only to work on values, so you can first array_flip and then use array_filter.

array_flip(array_filter(array_flip($data), create_function('$a','return $a%2;')))

Answer 4

foreach($arr as $key => $value) if($key&1) unset($arr[$key]);

The above removes odd number positions from the array, to remove even number positions, use the following:

Instead if($key&1) you can use if(!($key&1))

Answer 5

You could also use SPL FilterIterator like this:

class IndexFilter extends FilterIterator {
    public function __construct (array $data) {
        parent::__construct(new ArrayIterator($data));
    }   

    public function accept () {
        # return even keys only
        return !($this->key() % 2);
    }     
}

$arr      = array('string1', 'string2', 'string3', 'string4');
$filtered = array();

foreach (new IndexFilter($arr) as $key => $value) {
    $filtered[$key] = $value;
}

print_r($filtered);

Answer 6

<?php
function odd($var)
{
    // returns whether the input integer is odd
    return($var & 1);
}

function even($var)
{
    // returns whether the input integer is even
    return(!($var & 1));
}

$array1 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
$array2 = array(6, 7, 8, 9, 10, 11, 12);

echo "Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>

Odd :
Array
(
    [a] => 1
    [c] => 3
    [e] => 5
)
Even:
Array
(
    [0] => 6
    [2] => 8
    [4] => 10
    [6] => 12
)