r - dplyr mutate refer new column itself

Question

I have a data frame like this named \'a\'.

   ID        V1
   1         -1 
   1          0 
   1          1 
   1        1000 
   1          0 
   1          1
         


        

Answer 1

This should work:

a %>% group_by(ID) %>% mutate(V2 = ifelse(row_number() == 1, 1, 0) + 
                                ifelse(row_number() > 1 & V1 <= 1000, 1, 0) + 
                                cumsum(ifelse(V1 >= 1000, 1, 0)))

Update: Changed second ifelse logic statement from row_number() > 1 & V1 < 1000 to that shown above. This alteration should give the results as requested in the comments.