We need to find the index of the element in the nested array, where the elements are constructed as follows:

array = [
  index = & gt; [line1, line2]
]

Moreover, the search string is checked against the string1 element of this array. It was thought that the following construction could be passed as the first parameter: [string, '(. *)'] , where (. *) is any string. Why doesn’t it work?

$ arr = [
  '1' = & gt; ['a', '1'],
  '2' = & gt; ['b', '2']
];
echo array_search (['a', '(. *)'], $ arr);

Answer 1, authority 100%

echo array_search (['a', '(. *)'], $ arr);

The specified construct searches for an element with the value ['a', '(. *)'] in the $ arr array.

The first $ needle parameter in array_search is the value to search.

Naturally, there is no such value in the $ arr array, so the result is array_search false.

Can you tell us in more detail what exactly from such an array you need to find?

$ arr = [
  '1' = & gt; ['a', '1'],
  '2' = & gt; ['b', '2']
];

If you want to find the index of the element ‘b’:

foreach ($ arr as $ index = & gt; $ value) {
  if (is_array ($ value)) {
    if (($ i = array_search ('b', $ value))! == false) {
      echo 'First index:'. $ index. PHP_EOL;
      echo 'Second index:'. $ i. PHP_EOL;
      var_dump ($ arr [$ index] [$ i]); // element to search for
    }
  }
}

Answer 2

class SearchArray {
 private $ param = null;
 public function __construct ($ search) {
  $ this- & gt; param = $ search;
 }
 public function searchArray ($ a) {
   if (array_search ($ this- & gt; param, $ a)! == false) {
    return true;
   }
 }
}
$ math = array_filter ($ arr, array (new SearchArray ('a'), 'searchArray'));
var_dump ($ math);

you can try it.