How to split a string in PHP at nth occurrence of needle?

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David (imported from SE)

There must be a fast and efficient way to split a (text) string at the "nth" occurrence of a needle, but I cannot find it. There is a fairly full set of functions in the [strpos comments in the PHP manual](http://www.php.net/manual/en/function.strpos.php#102336), but that seems a bit much for what I need.

I have plain text as `$string`, and want to split it at *nth* occurrence of `$needle`, and in my case, `needle` is simply a space. (I can do the sanity checks!)

Can someone point me in the right direction? Many thanks!

Top Answer

Galled (imported from SE)

Could be?

    function split2($string,$needle,$nth){
    $max = strlen($string);
    $n = 0;
    for($i=0;$i<$max;$i++){
    	if($string[$i]==$needle){
    		$n++;
    		if($n>=$nth){
    			break;
    		}
    	}
    }
    $arr[] = substr($string,0,$i);
    $arr[] = substr($string,$i+1,$max);
    
    return $arr;
    }

Answer #2

Jack Douglas

You can use recursion to do this too:

```
function strposn(string $haystack, string $needle, $nth, $offset = 0){ return $nth?strposn($haystack,$needle,$nth-1,strpos($haystack,$needle,$offset)+1):$offset; }

$my_string = 'one two three four five six';
$split_pos = strposn($my_string,' ',4);
echo 'left: "'.substr($my_string,0,$split_pos-1).'"'.PHP_EOL;
echo 'right: "'.substr($my_string,$split_pos).'"'.PHP_EOL;
```

produces:

```none
left: "one two three four"
right: "five six"
```

If you care what happens when passing in either 0 or a number higher than the actual number of occurrences you may need to add some checking.

Answer #3

Vardkin (imported from SE)

I really like Hamze GhaemPanah's [answer][1] for its brevity. However, there's a small bug in it. 

In the original code:
```
$i = $pos = 0;    
do {
        $pos = strpos( $string, $needle, $pos+1 );
} while( $i++ < $nth);
```

`$nth` in the `do while` loop should be replaced with `($nth-1)` as it will incorrectly iterate one extra time - setting the `$pos` to the position of the `$nth+1` instance of the needle. Here's an example [playground to demonstrate][2]. If this link fails here is the code:

```
$nth = 2;
$string = "44 E conway ave west horse";
$needle = " ";

echo"======= ORIGINAL =======\n";

$i = $pos = 0;    
do {
        $pos = strpos( $string, $needle, $pos+1 );
} while( $i++ < $nth);

echo "position: $pos \n";
echo substr($string, 0, $pos) . "\n\n";

/* 
    Outputs:

    ======= ORIGINAL =======
    position: 11 
    44 E conway
*/

echo"======= FIXED =======\n";

$i = $pos = 0;    
do {
    $pos = strpos( $string, $needle, $pos+1 );
} while( $i++ < ($nth-1) );

echo "position: $pos \n";
echo substr($string, 0, $pos);

/*
    Outputs:

    ======= FIXED =======
    position: 4 
    44 E

*/
```

That is, when searching for the position of the 2nd instance of our needle, our loop iterates one extra time setting `$pos` to the position of our 3rd instance of our needle. So, when we split the string on the 2nd instance of our needle - as the OP asked - we get the incorrect substring.

Kudos to Hamze for the clever answer.

  [1]: /php?q=1071#a1290
  [2]: https://www.tehplayground.com/vAutCoJvXvqRBWAu

Answer #4

Hamze GhaemPanah (imported from SE)

Easily, just do it: (updated!)

    $i = $pos = 0;    
    do {
            $pos = strpos( $string, $needle, $pos+1 );
    } while( ++$i < $nth);

Answer #5

John (imported from SE)

If your needle will always be 1 character, use Galled's answer, it's going to be faster by quite a bit.  If your $needle is a string, try this.  Seems to work fine.

	function splitn($string, $needle, $offset)
	{
		$newString = $string;
		$totalPos = 0;
		$length = strlen($needle);
		for($i = 0; $i < $offset; $i++)
		{
			$pos = strpos($newString, $needle);
	
			// If you run out of string before you find all your needles
			if($pos === false)
				return false;
			$newString = substr($newString, $pos+$length);
			$totalPos += $pos+$length;
		}
		return array(substr($string, 0, $totalPos-$length),substr($string, $totalPos));
	}

Answer #6

LWC (imported from SE)

Taking [Matthew's answer][1] and adding a solution for [Dɑvïd's comment][2]:

    function split_nth($str, $delim, $n) {
      $result = array_map(function($p) use ($delim) {
          return implode($delim, $p);
      }, array_chunk(explode($delim, $str), $n));
      $result_before_split = array_shift($result);
      $result_after_split = implode(" ", $result); 
      return array($result_before_split, $result_after_split);
    }

Just call it by:

    list($split_before, $split_after) = split_nth("1 2 3 4 5 6", " ", 2);

Output:

    1 2
    3 4 5 6


  [1]: https://stackoverflow.com/a/5956463/4829915
  [2]: https://stackoverflow.com/questions/5956066/how-to-split-a-string-in-php-at-nth-occurrence-of-needle/5956463#comment6869588_5956463

6 Answers