LOOKUP Gives Wrong Value?

Hello,

I'm using LOOKUP to do something simple, but it appears to be giving a wrong (or I should say, at least unexpected) result some of the time.

I have a simple table where row 1 has four names in cols A through D (say "First", "Second", "Third", and "Fourth"). In rows 2 through 16, I have placed an "X" in one or more of the cells in each row. I followed a binary pattern to account for all combinations of X. For example row 2 has blank,blank,blank,X. Row 12 has X,blank,X,X. Row 16 has X,X,X,X.

In col E, for each row 2 through 16, I have the following formula:

=LOOKUP("X",A2:D2,$A$1:$D$1)

Every row in col E gives me the right answer except for two:
row 6 (blank,X,blank,X) gives me "Second" where I expected "Fourth".
row 14 (X,X,blank,X) gives me "Second" where I expected "Fourth".

I don't understand this as there are other rows with blanks in col C, yet it returns what I expect. For example:
row 10 (X,blank,blank,X) gives the expected value of "Fourth".

I tried this with MATCH too, and those same two locations give me the same unexpected index.

Can someone please explain this? I just want to get the col value in the first row that corresponds to the last "X" in each row.

Thanks, and sorry this description is so long. Harder to explain than to just look at!
Tony

lookup - needs to be sorted in ascending order to give the correct result - is that the issue at all

I don't really know. How is an empty cell sorted as compared to a cell with "X" in it?

Why would (X, blank, blank, X) work but not (X, X, blank, X)?

This is really strange, but it has to have something to do with the spacing. It's giving you the right-most x when there are two consecutive x's and then a space. So, x-x-blank-x is second, but x-blank-x-x is fourth. I added a fifth row to check and it's doing the same thing, but on the third consecutive x. So, x-x-blank-x-x is correctly giving me fifth, but x-x-x-blank-x is giving me third. It stops looking once it hits that space.

I know, right? It also works when you have two blanks in a row, like x-blank-blank-x gives Fourth!

Hey now Kevin, that worked! Thank you!

But why does that work?