Dealing with duplicated data in a CSV file

[bts001]

I am new to the programming world and I am looking for advice on the scenario below:

I have a csv file with four columns of data and I want to extract specific cells within the file. I want to do this through these steps:
1) Analyze the first column for duplicates
2) Using the first duplicate row, extract the value in the second and third column.
3) Store the extracted data in a new column or seperate csv file
4) Repeat for all duplicates

Note: I am not trying to remove duplicates, in fact I am trying to target them and keep only the first duplicate row of each.

What would be the easiest way to approach this?

Thanks!