Extracting Array Elements Based on Prefix Availability

In a scenario where you have an array with varying key prefixes, extracting only elements that start with a particular prefix can be a useful task. Let's consider an example array:

array(
  'abc' => 0,
  'foo-bcd' => 1,
  'foo-def' => 1,
  'foo-xyz' => 0,
  // ...
)

Challenge: Retain only elements starting with 'foo-'.

Functional Approach:

$array = array_filter($array, function($key) {
    return strpos($key, 'foo-') === 0;
}, ARRAY_FILTER_USE_KEY);

The array_filter function with the anonymous function checks if the key of each element starts with 'foo-'. If this condition is met, the element is retained in the modified array.

Procedural Approach:

$only_foo = array();
foreach ($array as $key => $value) {
    if (strpos($key, 'foo-') === 0) {
        $only_foo[$key] = $value;
    }
}

This approach iterates over the array, checking each key for the 'foo-' prefix. If found, the element is added to a new array containing only those elements that meet the criterion.

Procedural Approach Using Objects:

$i = new ArrayIterator($array);
$only_foo = array();
while ($i->valid()) {
    if (strpos($i->key(), 'foo-') === 0) {
        $only_foo[$i->key()] = $i->current();
    }
    $i->next();
}

With this approach, an ArrayIterator object is used to traverse the original array. Each key is inspected for the 'foo-' prefix, and corresponding elements are added to a new array.