Oh yes, I stand corrected. I didn't look at your code carefully enough. -- Bert
On Fri, Aug 10, 2012 at 3:07 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > On Aug 10, 2012, at 12:57 PM, Bert Gunter wrote: > >> ... or perhaps even simpler: >> >>> sz <- function(x,k)tapply(x,(seq_along(x)-1)%/%k, sum) >>> sz(1:10,3) >> >> 0 1 2 3 >> 6 15 24 10 >> >> Note that this works for k>n, where the previous solution does not. >>> >>> sz(1:10,15) >> >> 0 >> 55 > > > I agree that it is more elegant, but I do not get an error or an unexpected > result with my method. > >> N=10 >> k=15 >> w <- tapply( v ,rep(1:(N/k +1), each=k, len=N ) , sum) >> w > 1 > 55 > > A different label but the same result. I'm protected from the typical 1:0 > problem that seq_along solves by including +1 in the second argument to > ":"/seq(). Unless, of course, you set N to a negative number, but that > wouldn't make much sense would it, and you get an error from rep() anyway. > > Best; > David. > >> >> -- Bert >> >> On Fri, Aug 10, 2012 at 12:37 PM, David Winsemius >> <dwinsem...@comcast.net> wrote: >>> >>> >>> On Aug 10, 2012, at 12:20 PM, Sam Steingold wrote: >>> >>>> I have a long numeric vector v (length N) and I want create a shorter >>>> vector of length N/k consisting of sums of k-subsequences of v: >>>> >>>> v <- c(1,2,3,4,5,6,7,8,9,10) >>>> >>>> N=10, k=3 >>>> ===> [6,15,24,10] >>>> >>>> I can, of course, iterate: >>>> >>>>> w <- vector(mode="numeric",length=ceiling(N/k)) >>>>> for (i in 1:length(w)) w[i] <- sum(v(i*k:(i+1)*k)) >>>> >>>> >>>> >>>> (modulo boundary conditions) >>>> but I wonder if there is a better way. >>> >>> >>> >>> Well, using v with parentheses instead of square-brackets might not be >>> the >>> right way, since v is not a function. >>> >>> Consider this alternate (no need to pre-allocate 'w'): >>> >>>> w <- tapply( v ,rep(1:(N/k +1), each=k, len=N ) , sum) >>>> w >>> >>> 1 2 3 4 >>> 6 15 24 10 >>> >>> -- >>> >>> David Winsemius, MD >>> Alameda, CA, USA >>> >>> ______________________________________________ >>> R-help@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-help >>> PLEASE do read the posting guide >>> http://www.R-project.org/posting-guide.html >>> and provide commented, minimal, self-contained, reproducible code. >> >> >> >> >> -- >> >> Bert Gunter >> Genentech Nonclinical Biostatistics >> >> Internal Contact Info: >> Phone: 467-7374 >> Website: >> >> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm > > > David Winsemius, MD > Alameda, CA, USA > -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
