Question

PROBLEM

I have a nested PHP array that I need to populate from flat scalar
values. The problem is I cannot know ahead of time what the structure
of the nested PHP array will be until I get the request to fill in
the flat scalar values.

EXAMPLE

// example where we populate the array using standard PHP
$person['contact_info']['fname']  = 'Attilla';
$person['contact_info']['lname']  = 'Hun';
$person['contact_info']['middle'] = 'The';    
$person['hobbies'][0]             = 'Looting';
$person['hobbies'][1]             = 'Pillaging';

// example where we populate the array from flat scalar values
// (these are obtained from the user via name-value pairs)

// how can I correctly populate $person from this??
print($_GET['contact_info.fname']);   // 'Smokey';
print($_GET['contact_info.middle']);  // 'The';
print($_GET['contact_info.lname']);   // 'Bear';

// how can I correctly populate $person from this??
print($_GET['contact_info.fname']);   // 'Jabba';
print($_GET['contact_info.middle']);  // 'The';
print($_GET['contact_info.lname']);   // 'Hutt';

// How can I use these three flat scalars 
// to populate the correct slots in the nested array?

QUESTION

I know I must not be the first person who has needed to convert from flat name-value pairs into a nested PHP array (or nested array in any programming language). What is the established way (if any) of converting these flat scalar name-value pairs into the appropriate PHP nested array?

Just to re-iterate, I cannot know ahead of time what the name-value pairs will be for populating the array, that is one constraint I am dealing with here.

UPDATE

The fact that I cannot know the values (or, if you prefer, the Array keys that get populated by the scalar-value-representations) is a constraint of the particular problem space I am dealing with. This is not a question about basic PHP array syntax.

Answer 1

Note: My PHP code below is a hack, instead do this. Someone had posted a better solution earlier, but the post is gone now. In short, you can already submit arrays of values in forms to PHP:

<form ...>
<input type="text" name="contact_info[fname]">
<input type="text" name="contact_info[lname]">
<input type="text" name="contact_info[middle]">
</form>

The square brackets in the name attribute do exactly what you think they might do. On submit, $_POST['contact_info'] will be an array with three keys, fname, lname, and middle.

If at all possible, you should use this method rather than the code I’ve written below. It’s cleaner, it’s better, it’s more maintainable, it’s the way it should be done.

---

This is a fun challenge. We’re going to use PHP’s funny way of doing references to our advantage. Given that:

• $input is an array that contains only key/value pairs that are for $person
• A period is always the separator character
• You will never encounter a key that has both array and non-array values, i.e. there will never be both ‘contact_info’ and ‘contact_info.foo’

Then this function might be a starting point for you.

function nifty_splitty_magicky_goodness($input) {
// Start out with an empty array.
    $person = array();
    foreach($input as $k => $v) {
    // This turns 'a.b' into array('a', 'b')
        $key_parts = explode('.', $k);
    // Here's the magic.  PHP references aren't to values, but to
    // the variables that contain the values.  This lets us point at
    // array keys without a problem.  Sometimes this gets in the way...
        $ref = &$person;
        foreach($key_parts as $part) {
        // If we didn't already turn the thing we're refering to into an array, do so.
            if(!is_array($ref))
                $ref = array();
        // If the key doesn't exist in our reference, create it as an empty array
            if(!array_key_exists($part, $ref))
                $ref[$part] = array();
        // Reset the reference to our new array.
            $ref = &$ref[$part];
        }
    // Now that we're pointing deep into the nested array, we can
    // set the inner-most value to what it should be.
        $ref = $v;
    }
    return $person;
}

// Some test data.    
$input = array(
    'a.b' => 1,
    'a.c' => 2,
    'a.d.e' => 3,
    'f' => 4,
    'g.h' => 5
);
// Run it!
var_export(nifty_splitty_magicky_goodness($input));
// Should produce:
array (
  'a' => 
  array (
    'b' => 1,
    'c' => 2,
    'd' => 
    array (
      'e' => 3,
    ),
  ),
  'f' => 4,
  'g' => 
  array (
    'h' => 5,
  ),

Again, this is a hack. You should use PHP form handling to take care of this for you.