I have 2 datasets (new and old). Both have almost the same column names. The "old" dataset has variable_name_old. For example, the "new" dataset has a column named, Visit. In the "old" dataset, it will be named Visit_old. However, the old dataset has one variable name that is the same as the variable name in the "new" dataset. That is the sample_id1 variable. This is named the same way in both datasets for join purpose. However, after joining the 2 datasets, all columns in the old dataset duplicated. I will have Visit_old[1] and Visit_old[2]. The Visit_old[1] will have the original value from the old dataset. But the Visit_old[2] will have the Visit value from the new dataset. what could be causing the duplicate columns in the old dataset? Below is a screenshot of columns that are duplicated. Will appreciate any help! Please feel free to let me know if you need additional details! Thank you!