Hello all,

I am trying to find if there are any duplicate values within the same
column, without removing them. Example

ID no.
1121
2222
3343
5554
6785
4565
6785
1121
3343

In this example 1121, 3343, 6785 are duplicates. I have a ~20000 rows
spreadsheet and would like to speed up the process.

Thank you all,

Frank