匹配一组匹配中的第一个字符

Question

I have strings for date formats which will contain Y, M and D. For example some formats might be:

YY-MM-DD
M-D-Y G
MM/Y/DD
(etc)

I would like to run a regex match on strings like that and extract the Y, M, D in order. For example, in the above, I would like to have:

array('Y', 'M', 'D');
array('M', 'D', 'Y');
array('M', 'Y', 'D');
(etc)

I have written this regex expresion:

/(m+)|(d+)|(y+)/

But the issue is that it returns the whole match and not the first character like so:

array('YY', 'MM', 'DD');
array('M', 'D', 'Y');
array('MM', 'Y', 'D');
(etc)

How can I write my expression so that it only returns the first character?

Edit: some code (nothing complicated really).

$dates = array('YY-MM-DD', 'M-D-Y G', 'MM/Y/DD');

foreach($dates as $date){
   preg_match_all('/(m+)|(d+)|(y+)/', strtolower($date), $matches);
   var_dump($matches);
}

Answer 1

Looks to me like /\b[ymd]/ is all you need:

$dates = array('YY-MM-DD', 'M-D-Y G', 'MM/Y/DD');

foreach($dates as $date){
   preg_match_all('/\b[ymd]/', strtolower($date), $matches);
   var_dump($matches);
}

---

EDIT: Here's one that handles YYYYMMDD as well:

/(?<!y)y|(?<!m)m|(?<!d)d/

---

output:

array(1) {
  [0]=>
  array(3) {
    [0]=>
    string(1) "y"
    [1]=>
    string(1) "m"
    [2]=>
    string(1) "d"
  }
}
array(1) {
  [0]=>
  array(3) {
    [0]=>
    string(1) "m"
    [1]=>
    string(1) "d"
    [2]=>
    string(1) "y"
  }
}
array(1) {
  [0]=>
  array(3) {
    [0]=>
    string(1) "m"
    [1]=>
    string(1) "y"
    [2]=>
    string(1) "d"
  }
}