Filter array - odd even - php

Question

How can a filter out the array entries with an odd or even index number?
Array
(
[0] => string1
[1] => string2
[2] => string3
[3] => string4
)
Like, i want it remove the [0] and [2] entries from the array.
Or say i have 0,1,2,3,4,5,6,7,8,9 - i would need to remove 0,2,4,6,8.

Answer 1

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 2

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 3

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 4

<?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
)

Answer 5

I'd do it like this...
for($i = 0; $i < count($array); $i++)
{
if($i % 2) // OR if(!($i % 2))
{
unset($array[$i]);
}
}

Answer 6

<?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 7

$array = array(0 => 'string1', 1 => 'string2', 2 => 'string3', 3 => 'string4');
// Removes elements of even-numbered keys
$test1 = array_filter($array, function($key) {
return ($key & 1);
}, ARRAY_FILTER_USE_KEY);
// Removes elements of odd-numbered-keys
$test2 = array_filter($array, function($key) {
return !($key & 1);
}, ARRAY_FILTER_USE_KEY);
This answer is a bit of an improvement over this answer. You can use anonymous functions instead of create_function. Also, array_filter takes an optional flag parameter that lets you specify that the callback function takes the key as its only argument. So you don't need to use array_flip to get an array of keys.