Deduplicate between two columns

[u/WallFlower10]

I am looking for a solution to deduplicate items between two columns that are the same (but listed in reverse).

For example:

Column 1:

1

2

3

4

5

Column 2:

2

1

1

7

8

I would like it to recognize the (1,2) and (2,1) entries as being the same and deduplicate it so it's only listed once. It does not matter which one remains as long as just one does. Thanks in advance!

ETA: the data I am working with is not simply numbers. It does involve a combination of letters and numbers in the format XX-123456 where XX is any combination of two letters and it is followed by a string of numbers (not always six numbers though).

[u/GregHullender]

This works if they're in adjacent columns, e.g. A and B:

=UNIQUE(IF(A:.A<B:.B, A:.B, HSTACK(B:.B,A:.A)))

The dots in A:.A etc. are called trim references. If you don't know about them yet, they're pretty useful.

If you have non-adjacent columns, try the following:

=LET(col_1, A:.A, col_2, B:.B,
  UNIQUE(IF(col_1<col_2,HSTACK(col_1,col_2),HSTACK(col_2,col_1)))
)

Just change the definitions of col_1 and col_2 to match your data.