Creating Data Table...only adding another row when it does not already exist

I have a situation that is probably rather common; however, I am not sure the best way to remedy.

We have a spreadsheet of 1000’s of rows and each row has a name in the “User” column. For each name, we need to grab the appropriate organization and append that data to the same row. If this was the only task, it would be pretty simple. The issue I’d like to address is the possibility of a single “User” showing up numerous times. If the automation had already looked up a specific “User” I don’t want to go back and get the same information again. I think the answer is going to be create a data table on the back end that has a User column and an org column. And then for each row, reference the data table to see if the user name exists already and go from there.

My questions are:
Does this sound like the best option?
If so, what’s the best way to create/reference the data table?

Thank you!



Can you share input excel and output excel you required?

That will help to understand your case