group ordered line numbers

Question

I have some data that I am trying to group by consecutive values in R. This solution is similar to what I am looking for, however my data is structured like this:

line_num
1
2
3
1
2
1
2
3
4

What I want to do is group each time the number returns to 1 such that I get groups like this:

line_num	group_num)
1	1
2	1
3	1
1	2
2	2
1	3
2	3
3	3
4	3

Any ideas on the best way to accomplish this using dplyr or base R? Thanks!

score 2 · Accepted Answer · answered Jul 28 '21 at 22:50

We could use cumsum on a logical vector

library(dplyr)
df2 <- df1 %>%
    mutate(group_num = cumsum(line_num == 1))

or with base R

df1$group_num <- cumsum(df1$line_num == 1)

data

df1 <- structure(list(line_num = c(1L, 2L, 3L, 1L, 2L, 1L, 2L, 3L, 4L
)), class = "data.frame", row.names = c(NA, -9L))

group ordered line numbers

1 Answers1

data