How do I find matched cells in rows in a dataframe

I need to detected matched cells in the 3rd column.
For example : there is 2 column with "Amoxicillin...Clavulanate, Imipenem".
My data set is about 30000 record and I need to find records with matching items in the 3rd column.

The group_by() function in the dplyr package will tag groups of rows that have the same value in a column. If yourdata frame is named DF, running

DF <- DF |> group_by(columns_non_susceptible)

will give you a grouped data frame. But the grouping is internal and you will need other functions to do something with those groups. What is you goal?