A little while ago i was give this formula to help me re-order a list based on the fact that it is mixed letters & numbers. IE if a letter "R" is in the list then it becomes 1, if in the same list a 1 appears this becomes a 2 & so on
=IF(A1="R",1,IF(A1=0,MAX(A$1:A$11)+COUNTIF(A$1:A1,0)+1,A1+1))...