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

We can try

a %>%
     group_by(ID) %>% 
     mutate(V2 = cumsum(V1 >= 1000)+1L)
#     ID    V1    V2
#  <int> <int> <int>
#1     1    -1     1
#2     1     0     1
#3     1     1     1
#4     1  1000     2
#5     1     0     2
#6     1     1     2
#7     2    -1     1
#8     2     0     1
#9     2  1000     2

data

a <- structure(list(ID = c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L), 
V1 = c(-1L, 
0L, 1L, 1000L, 0L, 1L, -1L, 0L, 1000L)), .Names = c("ID", "V1"
), class = "data.frame", row.names = c(NA, -9L))

Answer 2

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.