Re: observation number

[Sundar Dorai-Raj <sundar.dorai-raj@pdf.com>]

Janusz Borkowski wrote:
> Dear S+ users,
> I have a data frame in which the first column indicates the day number, 
> the second column  observation number and the third results of 
> observations. It may look like:
> Dn    On    R1
> 1    1    3
> 1    2    4
> 1    3    5
> 2    4    6
> 2    5    7
> 2    6    8
> To find minimum value of R1 for each day is easy:
> min.valR1<-Tapply(R1,Dn,min)
> but how can I get not only the vector of minimum values, but also a 
> vector of observation numbers for which the minimum occurred I am using 
> S+ 4.5 for Windows.
> I will appreciate any advice.
Is this what you need?

dat <- data.frame(Dn = c(1, 1, 1, 2, 2, 2),
                  R1 = c(1, 0, 3, 5, 6, 4))
by(dat$R1, dat$Dn, function(x) {
  m <- min(x)
  c(m, which(x == m))
})

Regards,
Sundar