Remove every nth item from array - php

Question

I want to unset every second item from an array. I don't care about if the keys are reordered or not.
Of course I want it fast and elegant. Is it maybe possible without a loop and temporary variables?

Answer 1

My own solution so far:
for ( $i = 1; isset($arr[$i]); $i += 2) {
unset($arr[$i]);
}
The pro is, that it needs no if-statement, the con that a variable ($i) is still needed and it works only if the keys are numeric and without gaps.

Answer 2

function arr_unset_sec(&$arr, $key)
{
if($key%2 == 0)
{
unset($arr[$key]);
}
}
array_walk($arr, 'arr_unset_sec');
Assuming $arr may be some array. Check this piece of code.

Answer 3

If you have an array like
Array
(
[0] => test1
[1] => test2
[2] => test3
[3] => test4
[4] => test5
)
Then you can go with below code. It will remove every second item of array.
$i = 1;
foreach ($demo_array as $key => $row) {
if($i%2 == '0')
{
unset($demo_array[$key]);
}
$i++;
}
Hope this will helps you. Let mee know if you need any further help on it.

Answer 4

Another solution without a loop:
$arr = array('a', 'b', 'c', 'd', 'e');
$arr = array_filter( $arr, function($k) { return $k % 3 === 0; }, ARRAY_FILTER_USE_KEY);
Pro, it needs no loop. Cons, it is a lot slower than my other version (with a for loop), looks a bit scary and depends again on the keys.

Answer 5

I'll provide two methods (array_filter() and a foreach() loop) which will leverage the condition $i++%$n to target the elements to be removed.
Both methods will work on indexed and associative arrays.
$i++ This is post-incrementation. Effectively, the value will be evaluated first, then incremented second.
% This is the modulo operator - it returns the "remainder" from the division of the leftside value from the rightside value.
The return value from the condition will either be 0 or a positive integer. For this reason, php's inherent "type juggling" feature can be used to convert 0 to false and positive integers as true.
In the array_filter() method, the use() syntax must use &$i so that the variable is "modifiable". Without the &, $i will remain static (unaffected by post-incrementation).
In the foreach() method, The condition is inverted !() in comparison to the array_filter() method. array_filter() wants to know what to "keep"; foreach() wants to know what to unset().
Code: (Demo)
// if:$n=2 $n=3 $n=4 $n=5
$array=['first'=>1,
2, // remove
'third'=>3, // remove
'fourth'=>4, // remove remove
5, // remove
6, // remove remove
'seventh'=>7,
'eighth'=>8, // remove remove
'ninth'=>9]; // remove
// if $n is 0 then don't call anything, because you aren't attempting to remove anything
// if $n is 1 then you are attempting to remove every element, just re-declare as $array=[]
for($n=2; $n<5; ++$n){
$i=1; // set counter
echo "Results when filtering every $n elements: ";
var_export(array_filter($array,function()use($n,&$i){return $i++%$n;}));
echo "\n---\n";
}
echo "\n\n";
// Using a foreach loop will be technically faster (only by a small margin) but less intuitive compared to
// the literal/immediate interpretation of "array_filter".
for($n=2; $n<5; ++$n){
$i=1;
$copy=$array;
foreach($copy as $k=>$v){
if(!($i++%$n)) unset($copy[$k]); // or $i++%$n==0 or $i++%$n<1
}
echo "Results when unsetting every $n elements: ";
var_export($copy);
echo "\n---\n";
}
Output:
Results when filtering every 2 elements: array (
'first' => 1,
'third' => 3,
1 => 5,
'seventh' => 7,
'ninth' => 9,
)
---
Results when filtering every 3 elements: array (
'first' => 1,
0 => 2,
'fourth' => 4,
1 => 5,
'seventh' => 7,
'eighth' => 8,
)
---
Results when filtering every 4 elements: array (
'first' => 1,
0 => 2,
'third' => 3,
1 => 5,
2 => 6,
'seventh' => 7,
'ninth' => 9,
)
---
Results when unsetting every 2 elements: array (
'first' => 1,
'third' => 3,
1 => 5,
'seventh' => 7,
'ninth' => 9,
)
---
Results when unsetting every 3 elements: array (
'first' => 1,
0 => 2,
'fourth' => 4,
1 => 5,
'seventh' => 7,
'eighth' => 8,
)
---
Results when unsetting every 4 elements: array (
'first' => 1,
0 => 2,
'third' => 3,
1 => 5,
2 => 6,
'seventh' => 7,
'ninth' => 9,
)
---

Answer 6

$n = 1
for( $i=$n;$i=$n;)
{
unset($arOne[$i]);
unset($arSnd[$i]);
unset($arThd[$i]);
break;
}
I think this will also perfectly.