I need to remove only the unique data from a column and retain the duplicates. I cannot for the life of me find an answer online or figure it out.
I do not need to extract unique items, I do not need to remove duplicate items... I need to remove all unique (and the following colums) items and retain the duplicates.

5779423
5779431
5779432
5779440
5779453
5779459
5779462
5779462
5779503
5779523
5779524
5779545
5779573
5780158
5780162
5780162
5780221
5780263
5780285
5780293
5780294