Complex array merge

Question

I've been wrapping my head around this for a couple of days...

I have several arrays that need to be sort of merged into a single array. The order in which they merge is of great importance and is simply the order in which they appear in the global array (like the example below):

$input1 = array(
  array(
    'context' => 'aa', 'id' => 1, 'view' => 1, 'update' => 1,
  ),
  array(
    'context' => 'bb', 'id' => 2, 'view' => 0, 'update' => 0,
  )
);
$input2 = array(
  array(
    'context' => 'cc', 'id' => 3, 'view' => 0, 'update' => 1,
  ),
  array(
    'context' => 'dd', 'id' => 4, 'view' => 0, 'update' => 0,
  ),
  array(
    'context' => 'ee', 'id' => 5, 'view' => 1, 'update' => 0,
  )
);
$input3 = array(
  array(
    'context' => 'ff', 'id' => 6, 'view' => 1, 'update' => 1,
  ),
  array(
    'context' => 'gg', 'id' => 7, 'view' => 1, 'update' => 0,
  ),
);

$global = array($input1, $input2, $input3);

Each input array itself consists of several subarrays that are of equal structure; see http://pastebin.com/fQMUjUpB for an example. This pastebin code also includes the desired output. The output array should contain:

a single level array
a tree-like passthrough upon "merging the next input array", viz. every possible cross-combination of subarrays should be made during a merge between two input arrays
the key of each a combination should be generated as a concatenated string of the corresponding context and id elements (glued with a plus) joined together with an ampersand (&); e.g: context1+id1&context2+id2
For the next merge the previous resulting array should be used in order for the example from above becomes context1+id1&context2+id2&context3+id3
The resulting viewand update elements are calculated by simply multiplying their corresponding values during merge.

$output = array(
  'aa+1&cc+3&ff+6' => array('view' => 0, 'update' => 1),
  'aa+1&cc+3&gg+7' => array('view' => 0, 'update' => 0),
  'aa+1&dd+4&ff+6' => array('view' => 0, 'update' => 0),
  'aa+1&dd+4&gg+7' => array(...),
  'aa+1&ee+5&ff+6' => array(...),
  'aa+1&ee+5&gg+7' => array(...),
  'bb+2&cc+3&ff+6' => array(...),
  'bb+2&cc+3&gg+7' => array(...),
  'bb+2&dd+4&ff+6' => array(...),
  'bb+2&dd+4&gg+7' => array(...),
  'bb+2&ee+5&ff+6' => array(...),
  'bb+2&ee+5&gg+7' => array(...)
);

How can this be accomplished when looping over $global?

I may have expressed myself quite vaguely (it's really hard to explain!), but hopefully it becomes more clear when you take a look at the pastebin code...

Any help would be greatly appreciated!

You'll never have more than 3 input arrays into the $global array? — Maxime
– Maxime, Commented Nov 8, 2014 at 20:39
which algorithm are you use to get that index(like 'aa+1&cc+3&ff+6') in output array ? — Fas M
– Fas M, Commented Nov 8, 2014 at 20:41
@fasM For every cross-combination you make, always take context and id of a subarray, combine them with a plus sign and then concatenate it with the (existing) key of the resulting output array by using an ampersand. — Propaganistas
– Propaganistas, Commented Nov 8, 2014 at 20:48
@fasM those values are the result of multiplication of each subarray merge. So in the case of aa cc gg, then let's say for view it would be $aa['view'] * $cc['view'] * $gg['view'] — Propaganistas
– Propaganistas, Commented Nov 8, 2014 at 21:13

Maxime · Accepted Answer · 2014-11-09 11:26:23Z

2

Here's a minimal working code so that you can get the general idea (if you want to improve the code, feel free, there's a lot to do!):

function generate_output($globalArray, $context = array(), $view = 1, $update = 1, &$output = array()) {
    if(!count($globalArray)) {
        $output[implode('&', $context)] = array('view' => $view, 'update' => $update);
    }
    else {
        foreach(reset($globalArray) as $elt) {
            $newContext = $context;
            $newContext[] = $elt['context'] . '+' . $elt['id'];
            generate_output(array_slice($globalArray, 1), $newContext, $view * $elt['view'], $update * $elt['update'], $output);
        }
    }
    return $output;
}

generate_output($global);

edited Nov 9, 2014 at 11:26

answered Nov 8, 2014 at 21:07

Maxime

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5 Comments

Propaganistas Over a year ago

Done. I made some minor changes to your answer to generalize it even more.

Maxime Over a year ago

Thanks! Indeed, using a global variable is very ugly :)

Propaganistas Over a year ago

Another review is pending; instead of $globalArray[0] I suggested using reset($globalArray) to generalize the use case.

Propaganistas Over a year ago

Upon taking another look at the code, what's the point of using $newContext = array_slice($context, 0); instead of $newContext = $context;?

Maxime Over a year ago

There's no point, it's plain stupid. In PHP, arrays are assigned by copy anyway. Both expressions do the same thing, and $newContext = $context; is shorter and clearer. Go for it! I guess I just did a copy & paste from array_slice($globalArray, 1) without thinking much.

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