how to compare two files and identify duplicate values ?

There are so many ways to do this. 😏

Maybe the simplest, if you don't care for your output, is to use DuplicateFilter.

If your files are iterations of the same thing you can use ChangeDetector.

If you want to know which value came from which file you can use FeatureMerger where Merged and UsedSupplier are the "duplicate values", and, UnmergedRequestor and UnusedSuplier are the "unique values".

For better speed you can use FeatureJoiner almost the same way as the FeatureMerger.