PHP array question

Question

This is more of a conceptual question concerning the built in functionality of PHP and arrays. I was wondering if there is any way to do the following:

You have an array $a and this array contains 5 elements (0-4) for the purpose of this example.

Is there any way to make a new array, which would contain the following:

  $b[0] = $a[0];
  $b[1] = $a[0] + $a[1];
  $b[2] = $a[0] + $a[1] + $a[2];
  $b[3] = $a[0] + $a[1] + $a[2] + $a[3]; 
  $b[4] = $a[0] + $a[1] + $a[2] + $a[3] + $a[4];
  etc..

I imagine an example of it's use would be bread crumbs on a website, where you could click on any directory of a given link like /dir1/dir2/dir3/dir4

Is there anything built into PHP that can handle building up an array in this fashion? Or examples of a function which handles this? Or even a better way to go about this.

Thanks!

EDIT: Here is the final solution via the help of you guys! This will build the link, and create the proper link for each directory/element.

//$a is our array


$max = count($a);
foreach (range(1,$max) as $count) {
   $b[] = implode("/", array_slice($a, 0, $count));
}
foreach($b as $c) {
   $x = explode('/' , $c);
   $y = array_pop($x);
   echo "<a href='$c'>".$y."</a>"."/"; 
}

Answer 1

If you just want the five combinations as in your example then:

foreach (range(1,5) as $count) {
    $b[] = implode("/", array_slice($a, 0, $count));
}

Answer 2

You'd be best with a recursive function in that case.

$arr = array('dir1', 'dir2', 'dir3', 'dir4', 'dir5');

function breadcrumbs($a)
{
  // Remove first value
  $first = array_shift($a);

  // Loop through other values
  foreach ($a as $key => $value)
  {
    // Add first to remaining values
    $a[$key] = $first . '/' . $value;
  }

  // Return array
  return array($first) + breadcrumbs($a);
}

Untested, but should work. It will make each sequential value contain the values before it in the array.