[PHP] How to sort a Multidimensional array?

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Hi,
 
i have a multidimensional array that look like this:
$arr=array($key=>array('item0key'=>'item0', 'item1key'=>'item1',
'item2key'=>'item2', 'item3key'=>'item3', 'item4key'=>'item4'));
 
Lineview:
0    item0key = item0
      item1key = item1
      item2key = item2
      item3key = item3
      item4key = item4
 
1    item0key = item0
      item1key = item1
      item2key = item2
      item3key = item3
      item4key = item4
 
2    item0key = item0
      item1key = item1
      item2key = item2
      item3key = item3
      item4key = item4
 
4    item0key = item0
      item1key = item1
      item2key = item2
      item3key = item3
      item4key = item4
 
How can I sort such an array, depending on the Userentry by the Item values?
 
Thank you very much
Mirco Blitz