[R] Adding a column with a count of unique values

[arun]

Hi,
Try:
dat <- read.table(text="Person     Time     Change
2     0     3
2     10     5
2     15     7
3     0     4
3     5     2",sep="",header=TRUE)
dat1 <- transform(dat,Count= ave(rep(1,nrow(dat)), Person, FUN=cumsum))
#or
##If it is ordered by Person
dat2 <- transform(dat, Count= setNames(sequence(table(Person)),NULL))
#or
dat3 <- transform(dat,Count= ave(seq_along(Person), Person, FUN=seq_along))
all.equal(dat1,dat2)
#[1] TRUE
 all.equal(dat1,dat3)
#[1] TRUE

A.K.


I have a dataframe that looks like this:
Person     Time     Change
2     0     3
2     10     5
2     15     7
3     0     4
3     5     2
I would like to add a column that counts each row for each person, like this:
Person     Time     Change     Count
2     0     3     1
2     10     5     2
2     15     7     3
3     0     4     1
3     5     2     2
Thanks in advance!