Replace 3-letter month with its month number in an array of strings

Question

Search in the array for the first occurrence of a string until space, then convert it to month.

$arr = [
 "May Hello",
 "Jun Hello12",
 "Jul 3"
];

$str =  $arr[0];
$matches = [];
$pattern = '/^\w+\s/';
preg_match_all($pattern, $str, $matches);

Replace $pattern in $arr:

$pattern = [
 '/^\w+\s/' => date('m', strtotime($matches[0][0])) . ' ', // fist string until space
];
$arr = preg_replace(array_keys($pattern), array_values($pattern), $arr);

echo '<pre>';
print_r($arr);
echo '</pre>';

unexpected:

Array
(
    [0] => 05 7 Hello
    [1] => 05 Hello12
    [3] => 05 3
)

expected:

Array
(
    [0] => 05 7 Hello
    [1] => 06 Hello12
    [3] => 07 3
)

What am I doing wrong?

Answer 1

You should use preg_replace_callback when you want to run a function on the matched results:

$arr = [
 "May Hello",
 "Jun Hello12",
 "Jul 3"
];

$arr = preg_replace_callback(
        '/^(\w+)\s/',
        function ($matches) {
            return date('m', strtotime($matches[0])).' ';
        },
        $arr
    );

echo '<pre>';
print_r($arr);
echo '</pre>';

Output:

Array
(
    [0] => 05 Hello
    [1] => 06 Hello12
    [2] => 07 3
)