如何使用数组值的一部分作为新数组的键？

Question

How can I loop through an array and use part of the value as key for a new array?

Something like this:

$I = glob("path/to/file/*.txt");
foreach($I as $i){
    //key = function_acting_on($i) | value = $i
}

---

For example, when I do this:

$I = glob("path/to/file/*.txt");
foreach($I as $i){
    $new_array[] = $i;
}

This would automatically use numerical enumerated keys. But in my code I want to use part of the value $i as key.

array(4) {
  [0]=>
  string(3) "foo"
  [1]=>
  string(3) "bar"
  [2]=>
  string(5) "hello"
  [3]=>
  string(5) "world"
}

---

I used the accepted answer in the following way:

$images = glob("images/*.txt");
foreach( $images as $image ){
    preg_match('$pattern',$image,$match);
    $value = (int)preg_replace($pattern_,'',$match[0]);
    $array[$value] = $image;
    }
ksort($array);
var_dump($array);

Noticing now that duplicate keys are suppressed.

Answer 1

As you wrote in the comments, if you want to use a particular value as key of your array for a new array, you can simply do it like this:

$I = glob("path/to/file/*.txt");
$newArray = [];
foreach($I as $i){
    if(isset($newArray[function_acting_on($i)])){
        if(!is_array($newArray[function_acting_on($i)]))
            $newArray[function_acting_on($i)] = [$newArray[function_acting_on($i)]];
        $newArray[function_acting_on($i)][] = $i;
    } else {
    $newArray[function_acting_on($i)] = $i; 
            //^^^^^^^^^^^^^^^^^^^^^ Just use the return value as key
    }
}