Explode into all possible left-to-right combinations?

Question

Suppose I have a string, like so:

$string = 'president barack obama';

Now, suppose I want to explode this into an array, breaking at the words. You'd think I can just use explode(), right? That works, but what if I want an array of all possible left-to-right combinations of the words? Like so:

Array
(
    [0] => 'barack'
    [1] => 'barack obama'
    [2] => 'obama'
    [3] => 'president'
    [4] => 'president barack'
    [5] => 'president barack obama'
)

What is the most efficient way to do this?

Possible solution:

I've come up with one possible solution so far, but I'm hoping one of you can give me a better idea. I imagine approaching this like so:

Explode normally.
Loop through each word.
For each word, store it in an array. Then, check if there is another word in the array (after itself). If there is, add a new array value which consists of $current_word . ' ' . $new_word;. Do this for each word.

Now, that will probably work. However, it seems annoying, and I'm afraid someone else may have a better way of doing this. What do you all recommend? Is there, perhaps, a PHP function that does just this that I don't know about?

definitely there isn't native function for this – haynar Aug 07 '12 at 01:49 — haynar, Aug 07 '12 at 01:49
PHP has no such build-in functions. – xdazz Aug 07 '12 at 01:49 — xdazz, Aug 07 '12 at 01:49
Left-to-right parsing possibilities, thanks. :) – Nathanael Aug 07 '12 at 01:57 — Nathanael, Aug 07 '12 at 01:57

recursion.ninja · Accepted Answer · 2012-08-07T02:20:00.157

5

This should do what you are looking for:

$string  = 'president barack obama won';
$results = getWordPermutaions($string);
print_r($results);

function getWordPermutaions($inStr) {
  $outArr   = Array();
  $tokenArr = explode(" ", $inStr);
  $pointer  = 0;
  for ($i=0; $i<count($tokenArr); $i++) {
    $outArr[$pointer] = $tokenArr[$i];
    $tokenString = $tokenArr[$i];
    $pointer++; 
    for ($j=$i+1; $j<count($tokenArr); $j++) {
      $tokenString .= " " . $tokenArr[$j];
      $outArr[$pointer] = $tokenString;
      $pointer++;
    }
  }
  return $outArr;
}

/*
$results:
Array (
        [0] => 'president'
        [1] => 'president barack'
        [2] => 'president barack obama'
        [3] => 'president barack obama won'
        [4] => 'barack'
        [5] => 'barack obama'
        [6] => 'barack obama won'
        [7] => 'obama'
        [8] => 'obama won'
        [9] => 'won'
)
*/

edited Aug 07 '12 at 02:20

answered Aug 07 '12 at 02:05

recursion.ninja

5,377
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Thanks, but it doesn't appear to work. :P Test your code here: http://writecodeonline.com/php – Nathanael Aug 07 '12 at 02:15
I forgot a . on line 14, changed ` = ` to ` .= ` – recursion.ninja Aug 07 '12 at 02:19
too true, thanks for the [resource link](http://writecodeonline.com/php) , it has been bookmarked! – recursion.ninja Aug 07 '12 at 02:24

score 3 · Answer 2 · answered Aug 07 '12 at 02:29

Another working solution:

  $s = 'president barack obama won';

  function myExplode($s) {
    $ex = explode(" ", $s);
    $ec = 0;
    $x = 0;
    foreach ($ex as $word) {
      $rs = isset($res) ? sizeof($res) : 0;
      if ($rs > 0)
        for ($i=$ec-$x; $i < $rs; $i++) $res[] = "{$res[$i]} {$word}";
      $x++;
      $res[] = $word;
      $ec = sizeof($res);
      }
    return isset($res) ? $res : false;
    }

  print_r( myExplode($s) );

Output

Array
(
    [0] => president
    [1] => president barack
    [2] => barack
    [3] => president barack obama
    [4] => barack obama
    [5] => obama
    [6] => president barack obama won
    [7] => barack obama won
    [8] => obama won
    [9] => won
)

Explode into all possible left-to-right combinations?

Possible solution:

2 Answers2