Working within a Google Sheet, I have a list of people’s work locations or departments in Columns A or G, their names in Columns B or H, and their extensions in Columns C or I. It is formatted this way to be printed on a single letter-size paper in a practical “two-column” view.

I am using Sort and Unique to list all the four-digit extensions from Column C and Column I to make one flat list of all extensions in Column L, ultimately creating a reverse lookup by extension.

I have the formula working for a single column (Column C or Column I), e.g.: =SORT(UNIQUE(FILTER(C3:C,REGEXMATCH(TEXT(C3:C,”0000″),”^(d{4})$”)))) provides the expected results.

However, every attempt to combine the formula with both columns for a single list errors out or fails to give appropriate results.

Current formula attempting: =SORT({UNIQUE(FILTER(C3:C,REGEXMATCH(TEXT(C3:C,”0000″),”^(d{4})$”)))}&{UNIQUE(FILTER(I3:I,REGEXMATCH(TEXT(I3:I,”0000″),”^(d{4})$”)))}).

My results are an eight-digit combination of two different extensions.