Lining up sets of data in Excel (both with unique keys)

A related question asks how to line up two sets of data in Excel. I am struggling to figure out how to do this when you have values in both lists which don't exist in the other list. Ie: how would line up these lists?

Position    Occurrences
      8               3
     11               1
     17               2
     18               1

and another set of data has

Position    Occurrences
      8               1
      9               3
     18               6

how can I line it up so that it's

Position    Occurrences     Position    Occurrences
      8               3            8              1
                                   9              3
     11               1         
     17               2         
     18               1           18              6

You'll note that in this example we have Position's 11 and 17 which are in list 1 but not list 2. And Position 9 which is in list 2 but not list 1.

You need to create a master list containing all possible values (e.g. 1 to 20 in your case) and look for the corresponding values from the original list:
- fill numbers 1 - 20 in A2 to A21
- in column B put formula: =if(iserror(match(A2,<range1!column1>,0)),"",A2)
- formula in column C: =iferror(vlookup(A2,<range1!columns1:2>,2,false),"")
- in columns D and E put the same formulas related for your second range
- in column F put this formula to check whether any of the ranges has value in the row to let you filtering out empty rows: =count(C2,D2)>0