问题
I want to add an ordered ID (by date) to each group in a data frame. I can do this using dplyr (R - add column that counts sequentially within groups but repeats for duplicates):
# Example data
date <- rep(c("2016-10-06 11:56:00","2016-10-05 11:56:00","2016-10-05 11:56:00","2016-10-07 11:56:00"),2)
date <- as.POSIXct(date)
group <- c(rep("A",4), rep("B",4))
df <- data.frame(group, date)
# dplyr - dense_rank
df2 <- df %>% group_by(group) %>%
mutate(m.test=dense_rank(date))
group date m.test
<fctr> <dttm> <int>
1 A 2016-10-06 11:56:00 2
2 A 2016-10-05 11:56:00 1
3 A 2016-10-05 11:56:00 1
4 A 2016-10-07 11:56:00 3
5 B 2016-10-06 11:56:00 2
6 B 2016-10-05 11:56:00 1
7 B 2016-10-05 11:56:00 1
8 B 2016-10-07 11:56:00 3
So my new column m.test
ranks each group
by date
. If I use rleid
and data.table
, it doesn't seem to work (05/10 ranked after 06/10):
df3 <- setDT(df)[, m.test := rleid(date), by = group]
group date m.test
1: A 2016-10-06 11:56:00 1
2: A 2016-10-05 11:56:00 2
3: A 2016-10-05 11:56:00 2
4: A 2016-10-07 11:56:00 3
5: B 2016-10-06 11:56:00 1
6: B 2016-10-05 11:56:00 2
7: B 2016-10-05 11:56:00 2
8: B 2016-10-07 11:56:00 3
Am I getting the syntax wrong?
回答1:
Thanks to @docendo discimus, the correct way to do this with data.table
is frank(..., ties.method = "dense")
:
df4 <- setDT(df)[, m.test := frank(date, ties.method = "dense"), by = group]
来源:https://stackoverflow.com/questions/40588901/add-ordered-id-for-each-group-by-date