The notes for LOOKUP function indicate the values in a row must be sorted or
invalid results will occur. Is there a way to get around this? How can I
use the LOOKUP function or any other lookup function to correctly return
results on an unsorted row of data? Below is an example of what I need to
accomplish:

C1 - C4 are column headers (text values)

A B C D
1 C1 C2 C3 C4
2 5 3 2 4

=lookup(5,A2:D2,A1:D1)

Actual / Invalid Result: C4
Correct / Needed Result: C1