PHP - create multi-dimensional array from delimited string

PHP - create multi-dimensional array from delimited string

My original was deleted (I expect the same on this within days.)
I simply wanted to create a multi-dimensional array
$myArray['a']['b']['c']['d'] = null
from a delimited string,
a,b,c,d
but it seems I "broke some rules" (didn't supply previous code, asked for
a hand out). I will not bother listing the innumerable postings to this
board which broke the same rules but was treated in a civil manner, and
even got relevant answers!
I wish t thank "Armsless" for asking the same question, but in better
English (it's the only reason I can think of that he didn't get pummeled,
or was it because he has a "rep" on here.)
[http://stackoverflow.com/questions/1417019]
I also would like to thank "JasonWoof" for his thoughtful and relevant
response, your solution was spot on and taught me to look in more obvious
places (code wise) for solutions.