selecting data in Excel worksheet

Knowing more about the data would help. For example, to see if the data on the same row is duplicated would be easy. The formula IF(a1=b1,"dup","ok") in column c and copy down column c could be used. If it's duplicated, you would see dup in columnc, other wise you would see ok.

If however, you need to check for dups between a and b on any row it becomes harder. In that case you could use COUNTIF in column c. For example, the formula COUNTIF(B1:B999,A1) in c1 will tell you how many times the string from a1 occurs in column b. From there, you would have to search column b for any occurances.

Don

I agree that we need to know more.
But let?s make a guess:
Suppose you have a long list in Column A with rangename Acol, idem in B with Bcol.
In C1 you could use a formula like:
=vlookup(A1;Bcol;1;false)
In D1:
=vlookup(B1;Acol;1;false)
Select both cells, double click on the fill handle right bottom and the formulas will propagate.
If a value in A is also in B you will get that value in C etc.
Else you will get #N/A
Another solution is to name both ABcol
Put the following formula inE1:
=countif(Abcol;a1)
Copy formula to F1 and propagate both.
If a value would appear more than one time in any column you would get a count >1.
With auto-filter or other formula?s it is possible to sort out.
But again more is needed to know what exactly to do.
It may be necessary to link one column to another sheet and add formulas there in order not to loose data with an auto-filter and (custom ..)
Realise that with e.g. 5000 rows it may take several minutes to calculate all formulas!NOTE: your list divider may be , and not ;
Success!