php put arrays in arrays - php

Question

I want to push some items in one array, here is the structure:
$str = 'String';
$a = array('some', 'sub', 'page');
and I want to push the items to some other array that should become:
Array (
[some] => Array (
[sub] => Array (
[page] => String
)
)
)
I don't know how exactly to explain it, so hope the example shows you something.
I want any new element in the first array (a) to be pushed as sub-array of the prevous one and the last to have the value from $str;
$string = 'My Value';
$my_first_array = array('my', 'sub', 'arrays');
Then some function to parse $my_first_array and transfer it as:
Example:
ob_start('nl2br');
$my_parsed_sub_array = parse_sub_arrays($my_first_array, $string);
print_r($my_parsed_sub_array);
===>>>
Array (
[my] => Array (
[sub] => Array (
[arrays] => String
)
)
)

Answer 1

[Edit] I hope that, this time, I've understood the question...
If you have your string and array like this :
$str = 'test';
$a = array('some', 'sub', 'page');
You could first initialize the resulting array this way, dealing with that special case of the last item :
$arr = array($a[count($a)-1] => $str);
Then, you can loop over each item of your $a array, starting from the end (and not working on the last item, which we've dealt with already) :
for ($i=count($a) - 2 ; $i>=0 ; $i--) {
$arr = array($a[$i] => $arr);
}
With this, dumping the resulting array :
var_dump($arr);
Should get you the expected result :
array
'some' =>
array
'sub' =>
array
'page' => string 'test' (length=4)
Old answer below, before understanding the question :
You could declare your array this way :
$arr = array(
'some' => array(
'sub' => array(
'page' => $str,
),
),
);
Or, using several distinct steps (might be easier, depending on the way you construct your sub-arrays, especially in a more complex case than the current example) :
$sub2 = array('page' => $str);
$sub1 = array('sub' => $sub2);
$arr = array('some' => $sub1);