HI, Same result, with data.frame: dat1<-data.frame(V1=v[1:3],V2=v[4:6],V3=v[7:9],V4=c(v[10],rep(0,2))) sapply(dat1,cumsum)[3,] V1 V2 V3 V4 6 15 24 10 sapply(dat1,sum) V1 V2 V3 V4 6 15 24 10 A.K.
----- Original Message ----- From: David Winsemius <dwinsem...@comcast.net> To: Michael Weylandt <michael.weyla...@gmail.com> Cc: "r-help@r-project.org" <r-help@r-project.org>; "s...@gnu.org" <s...@gnu.org>; Bert Gunter <gunter.ber...@gene.com> Sent: Friday, August 10, 2012 6:58 PM Subject: Re: [R] summarize a vector On Aug 10, 2012, at 3:42 PM, Michael Weylandt wrote: > I wouldn't be surprised if one couldn't get an *apply-free solution by using > diff(), cumsum() and selective indexing as well. What about colSums on a matrix extended with the right number of zeros. > colSums(matrix (c(v, rep(0, 3- length(v)%%3) ) , nrow=3) ) [1] 6 15 24 10 (My experience is that tapply is generally fairly fast anyway, much faster than apply.data.frame. So I do not lump all *apply solutions in the same efficiency category.) --David. > > Cheers, > Michael > > On Aug 10, 2012, at 5:07 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 >> >> ______________________________________________ >> 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. 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. ______________________________________________ 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.
