+2-1+18*+7-21+3*-4-5+6x29

The above string is an example of the kind of string I'm trying to split into either a key => value array or something similar.

The numbers represent the id of a class and -,+ and x represent the state of the class (minimised, expanded or hidden), the * represents a column break.

I can split this into the columns easily using explode which gives and array with 3 $key => $value associations.

eg.

$column_layout = array( [0] => '+2-1+18' , [1] => '+7-21+3' , [2] => '-4-5+6x29' )

I then need to split this into the various classes from there, keeping the status and id together.

eg.

$column1 = array( '+' => 2 , '-' => 1 , '+' => 18 )
...

or

$column1 = array( array( '+' , 2 ) , array( '-' , 1 ) , array( '+' , 18 ) )
...

I can't quite get my head round this and what the best way to do it is, so any help would be much appreciated.