On 4/25/05, vincent <[EMAIL PROTECTED]> wrote: > > Dear all, > > First I apologize if my question is quite simple, > but i'm very newbie with R. > > I have vectors of the form v = c(1,1,-1,-1,-1,1,1,1,1,-1,1) > (longer than this one of course). > The elements are only +1 or -1. > > I would like to calculate : > - the frequencies of -1 occurences after 2 consecutives -1 > - the frequencies of +1 occurences after 2 consecutives +1 > > It looks probably something like : > Proba( Ut+2=1 / ((Ut+1==1) && (Ut==1))) > > could someone please give me a little hint about how > i should/could begin to proceed ?
Let v be a time series. Then lag(v, -1) is the same series moved forward by one and lag(v, -2) is the same series moved forward by two. Now we just want to know if all three are equal to -1 (or +1 in the other case): v <- ts(c(1,1,-1,-1,-1,1,1,1,1,-1,1)) sum( lag(v, -2) == -1 & lag(v,-1) == -1 & v == -1 ) sum( lag(v, -2) == 1 & lag(v,-1) == 1 & v == 1 ) Using ts objects in this way has the nice property that it takes care of alignment and end effects for you automatically. [[alternative HTML version deleted]] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html