#put all data frames into list df_list <- list(df1, df2, df3) #merge all data frames in list Reduce(function(x, y) merge(x, y, all=TRUE), df_list)
merge(x = df1, y = df2, by = c("Name_tag1", "Name_tag2"), all = TRUE)
merge(data.frame(A, row.names=NULL), data.frame(B, row.names=NULL), by = 0, all = TRUE)[-1]