[Rd] aggregate.ts (PR#514)

[plummer@iarc.fr]

aggregate.ts does not behave in the same way as the equivalent
method aggregate.rts in S-PLUS. In particular it
- changes the start of the time series
- tends to have a length which is 1 shorter

For example:

R> x <- ts(1:10)
R> aggregate(x, nfreq=0.5, FUN=min)
Time Series:
Start = 2 
End = 8 
Frequency = 0.5 
[1] 2 4 6 8

S> x <- rts(1:10)
S> aggregate(x, nf=0.5, fun = min)
[1] 1 3 5 7 9
 start deltat frequency 
     1      2       0.5

I have edited the aggregate.ts function to reproduce the S-PLUS
behaviour, which I find more intuitive:

old:
    #nstart <- ceiling(tsp(x)[1] * nfrequency)/nfrequency
    #x <- as.matrix(window(x, start = nstart))
new:    
    nstart <- tsp(x)[1]
    # Can't use nstart <- start(x) as this causes problems if
    # you get a vector of length 2.
    x <- as.matrix(x)

I have tried this on a range of examples and have not encountered
any problems, but of course I may be missing something.

Martyn

--please do not edit the information below--

Version:
 platform = i686-unknown-linux
 arch = i686
 os = linux
 system = i686, linux
 status =
 major = 1
 minor = 0.0
 year = 2000
 month = February
 day = 29
 language = R

Search Path:
 .GlobalEnv, Autoloads, package:base

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