Using SUMPRODUCT and OFFSET on multiple rows in Excel - excel

Question

I have a question on using OFFSET in Excel.
For instance, I have a table with values varying by years.
Then, I have a table with some values varying by year/months.
!!Click here for the tables!!
I would like to write a formula e.g.
=SUMPRODUCT((E2:E37)*OFFSET(A1,C2:C37,1),E2:E37)
but it returns #VALUE!
In short, I would like to use an array of values in C2:C37 i.e. {1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3} to obtain the array {0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.03,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.04,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,0.05,}, and this array is then used in the SUMPRODUCT function.
Can someone help me solve the #VALUE! issue?
Thanks in advance!

Answer 1

Apparently (I didn't know this) Offset is unusual because it can return a set of range objects when used with an array as the second argument. Most functions can't handle this if you pass it to them. But if you put it through the N function, you get the right answer.
=SUMPRODUCT((E2:E37)*N(OFFSET(A1,C2:C37,1)))
or
=SUMPRODUCT((E2:E37),N(OFFSET(A1,C2:C37,1)))
Note that these appear to give an array of #Value! errors when you run them through Evaluate Formula but these resolve after passing through the N function.
Of course it would be more common to do this the easy way and use Index or Vlookup with a helper column. My first thought when trying to do it in a single Array formula without using Offset was this:-
=SUM(E2:E37*MMULT(N(C2:C37=TRANSPOSE((ROW(A2:A4)-1))),B2:B4))
I would think that the Offset way is easier and more efficient.
But in this particular case where there are only a small number of categories you could use this array formula which is perhaps the simplest approach:-
=SUM(CHOOSE(C2:C37+1,0,B2,B3,B4)*E2:E37)
The above formulae only work for the special case where the 'key' is the same as the row number in the lookup column. The offset method can easily be adapted to incorporate a lookup:-
=SUM((E2:E37)*N(OFFSET(A1,IFERROR(MATCH(C2:C37,A2:A4,0),0),1)))
See this reference