Hello, I want to have some informations about the merge function: indeed, I want te merge many data frames but I don't want to have missing value NA for the rows but the number 0 for the rows who're not in all tables! I didn't see any options to do that!! and when I use function like na.omit and na.action to deal missing value (after merging all tables) and changing them in 0, after three hours I have no longer the results because I've got a data frame with 31 colonnes and more than 20000 rows. Do you have a solution for me, Thank you for answering, Nicolas BOUGET. [[alternative HTML version deleted]]