最有效的方法来查找重复值的位置php

Question

I would like to the most effective way to get the position of repeated elements element in array. For example, if i have:

$example = array('a','b','c','a','a','d');

So in this case 'a' is at position 0 - 3 - 4.

I know we can loop through but i think in it is ineffective. I would be grateful if you could show me a better way to do this.

Thank you very much

Answer 1

array_keys() with the optional search_value parameter

$example = array('a','b','c','a','a','d');

print_r(array_keys($example, "a"));

output:

Array ( [0] => 0 [1] => 3 [2] => 4 ) 

---

If you don't have a particular vlaue in mind and want the positions of all the values:

$example = array('a','b','c','a','a','d');



$out=array();
foreach($example as $k=>$v){

  $out[$v][]=$k;

}
echo '<pre>';

print_r($out);

returns:

Array
(
    [a] => Array
        (
            [0] => 0
            [1] => 3
            [2] => 4
        )

    [b] => Array
        (
            [0] => 1
        )

    [c] => Array
        (
            [0] => 2
        )

    [d] => Array
        (
            [0] => 5
        )

)