Thanks but I am sorry but I don't understand this solution. In my problem, I get a string s that user enters in a form. I append that to an empty list L = []

Thanks but I am sorry but I don't understand this solution. In my problem, I get a string s that user enters in a form. I append that to an empty list L = [] then I test if the last saved string is the same as the new string. If same, I write it on the same column; if not the cursor moves to next column (I was trying to do this with tables) and as long as the user types the same string the cursor stays on the same column. If a new string is typed; a new column is started; and so on. I don't think your solution is to this problem. You assume that there is a list with duplicates. Does this make sense?