I would only put the formula in rows that have entries--I'd copy the formula
down when I added more data.

But maybe you could just copy the formula down a bit more than you need and make
the formula return "" if the other data isn't there (yet).

=if(counta(a1:b1)=0,"",vlookup(a1&b1,sheet2!a:e,5, false))
or
=if(counta(a1:b1)<2,"",vlookup(a1&b1,sheet2!a:e,5, false))

(depending if filling one of those cells is sufficient.)

========
Another alternative to using concatenate...

You may be able to use something like:

=index(othersheet!$c$1:$c$100,
match(1,(a2=othersheet!$a$1:$a$100)*(b2=othersheet !$b$1:$b$100),0))
(one cell)

This is an array formula. Hit ctrl-shift-enter instead of enter. If you do it
correctly, excel will wrap curly brackets {} around your formula. (don't type
them yourself.)

Adjust the range to match--but you can't use the whole column.

This returns the value in othersheet column C when column A and B (of
othersheet) match A2 and B2 of the sheet with the formula.

And you can add more conditions by just adding more stuff to that product
portion of the formula:

=index(othersheet!$d$1:$d$100,
match(1,(a2=othersheet!$a$1:$a$100)
*(b2=othersheet!$b$1:$b$100)
*(c2=othersheet!$c$1:$c$100),0))

(still an array formula)

Max_power wrote:

Hello,

I'm having a problem concatenating two columns.
I have 2 empty columns, which I then want to concatenate once
information is populated into these fields. I then want to create a
list from these two concatenated columns and have this list as a lookup
on a different worksheet.
When I create the list I highlight the entire two columns as I don't
have a predefined number of entries for the two columns.

I've done this already but when I try and lookup any of the information
I get a blank list.

Can someone please advise me on any course of action
Do I need to use an isblank method?
Many many thanks

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Dave Peterson