Question

I got this multiple array named $files[], which consists of keys and values as below:

[
    [
        'name' => 'index1.php',
        'path' => 'http://localhost/php/gettingstarted/',
        'number' => 1,
    ],
    [
        'name' => 'index10.php',
        'path' => 'http://localhost/php/gettingstarted/',
        'number' => 2,
    ],
    [
        'name' => 'index11.php',
        'path' => 'http://localhost/php/gettingstarted/',
        'number' => 3,
    ],
]

I use this code to create a new array consist of ‘name’ keys only. But it failed

array_filter($files, "is_inarr_key('name')");

function is_inarr_key($array, $key)
{
    //TODO : remove every array except those who got the same $key
}

and I get this error:

array_filter() [function.array-filter]: The second argument, ‘is_inarr_key(‘name’)’, should be a valid callback in C:\xampp\htdocs\php\gettingstarted\index.php on line 15

So my questions are:

1. Is it possible to make the call-back function on array_filter receive parameter?
2. What is the general rule of thumb on how to use callback in any PHP built-in function?

Answer 1

You can create a closure on PHP ≥5.3.

array_filter($files, function($array) use ($key) {
  return is_inarr_key($array, $key); 
} );

---

If you are stuck with PHP <5.3, …

You can make $key a global variable.

function is_inarr_with_global_key($array) {
   global $key;
   ....
}

You can create a class

class KeyFilter {
  function KeyFilter($key) { $this->key = $key; }
  function is_inarr_key($array) { ... }
}
...
array_filter($files, array(new KeyFilter('name'), 'is_inarr_key'));

You can create 3 different functions

array_filter($files, 'is_inarr_name');
array_filter($files, 'is_inarr_path');
array_filter($files, 'is_inarr_number');

You can write your own array_filter

function my_array_filter($files, $key) {
  ...
}