Quickest way to restructure an array?

Question

I have an array which can have several items in it, e.g:

Item 1
Item 2
Item 3
Item 4
Item 5
Item 6
etc

I need the quickest way to restructure this array so that it has at most X items. So if I say that X is 3, the resulting array must be:

Item 1 , Item 2
Item 3, Item 4
Item 5, Item 6
etc

or if it has 7 items, it would be:

Item 1 , Item 2, Item 3,
Item 4, Item 5, 
Item 6, Item 7

What's the easiest way to do this?

I started with this, but it seems like there really must be an easier way:

foreach ($addressParts as $part)
{
    if (empty($part)) continue;
    if (empty($addressLines[$count]))  $addressLines[$count] = '';
    $addressLines[$count] .= $part;
    $count++;
    if ($count > 2) $count = 0;
}

Also, this won't work, because you will end up with this:

item 1, item 4, item 7
item 2, item 5
item 3, item 6

... which is wrong. Any thoughts?

UPDATE

If I start with:

Array
(
    [0] => item 1
    [1] => item 2
    [2] => item 3
    [3] => item 4
    [4] => item 5
    [5] => item 6
    [6] => item 7
)

I want to end with:

Array
(
    [0] => item 1, item 2, item 3
    [1] => item 4, item 5
    [2] => item 6, item 7
)

Make sense?

Answer 1

This function combines elements to a new array as per your example. It handles any number of input elements.

function ReduceArray($input, $length) {
        $frac = $length / count($input);
        $frac = $frac + 0.0001;    // Offset for float calculations
        $index = 0.0;

        // Copy the elements, rolling over on $index
        $temp = array();
        foreach ($input as $part) {
                $i= floor($index);
                if (!isset($temp[$i])) {
                        $temp[$i] = array($part);
                } else {
                        $temp[$i][] = $part;
                }
                $index += $frac;
        }

        // Combine the sub arrays
        $output = array();
        foreach ($temp as $line) {
            $output[] = implode(', ', $line);
        }
        return $output;
}

$input = array('Item 1',  'Item 2',  'Item 3',  'Item 4',  'Item 5',  'Item 6', 'Item 7');
$output = ReduceArray($input, 3);
print_r($output);

Output

Array
(
    [0] => Item 1, Item 2, Item 3
    [1] => Item 4, Item 5
    [2] => Item 6, Item 7
)

Edit "fixed" the output as per the given output.

Edit See Comment for nine elements, tested for up to 12 elements. Thanks sectus

Answer 2

For each group, calculate to offset of the first element and the group length, copy that slice from the input array.

function array_group_elements($array, $groups) {
  $result = array();
  $count = count($array);
  // minimum in each group
  $limit = floor($count / $groups);
  // balance, modulo
  $overhead = $count % $groups;
  // for each group
  for ($i = 0; $i < $groups; ++$i) {
    // group offset, add 1 for each group that got a balance element
    $offset = ($i * $limit) + ($i < $overhead ? $i : $overhead);
    // length, add 1 if it is a group with balance element
    $length = $limit + ($i < $overhead ? 1 : 0);
    // copy slice from original array
    $result[] = array_slice($array, $offset, $length);
  }
  return $result;
}

$input = array('Item 1',  'Item 2',  'Item 3',  'Item 4',  'Item 5',  'Item 6', 'Item 7');
$grouped = array_group_elements($input, 3);
var_dump(
  array_map(
    function($group) {
      return implode(', ', $group);
    },
    $grouped
  )
);

Output:

array(3) {
  [0]=>
  string(22) "Item 1, Item 2, Item 3"
  [1]=>
  string(14) "Item 4, Item 5"
  [2]=>
  string(14) "Item 6, Item 7"
}

The function array_group_elements() loops over the $groups (3 times), not the $array (7 times).