Hi,
p <- lapply(1:1e6, function(i)c(i, log2(i))) system.time(z1 <- t(sapply(p,function(x)x))) # user system elapsed # 2.568 0.048 2.619 system.time(z1 <- do.call(rbind,p)) # user system elapsed # 4.000 0.052 4.060 A.K. ----- Original Message ----- From: William Dunlap <wdun...@tibco.com> To: R. Michael Weylandt <michael.weyla...@gmail.com>; arun <smartpink...@yahoo.com> Cc: R help <r-help@r-project.org>; "s...@gnu.org" <s...@gnu.org> Sent: Tuesday, December 4, 2012 6:28 PM Subject: RE: [R] list to matrix? > No need for all this (see solutions including mine already given) -- > but even without those, this is silly. An identity map is a real waste > if you just want the simplification bit of sapply() -- you'd be much > better just using simplify2array() You are right that simplify2array(p) does everything that sapply(p,function(x)x) does and does it more quickly and that matrix(unlist(p),nrow=2,byrow=TRUE) is much faster than either: > p <- lapply(1:1e6, function(i)c(i, log2(i))) > system.time(z1 <- t(sapply(p,function(x)x))) user system elapsed 1.2 0.0 1.2 > system.time(z2 <- t(simplify2array(p))) user system elapsed 0.91 0.00 0.90 > system.time(z3 <- matrix(unlist(p), ncol=2, byrow=TRUE)) user system elapsed 0.04 0.00 0.04 You can also use vapply instead of sapply - it requires that you supply the expect shape and type of FUN's output so it is doesn't have to figure this out from looking at all the outputs of FUN: > system.time(z4 <- t(vapply(p,FUN=function(x)x,FUN.VALUE=numeric(2)))) user system elapsed 0.56 0.00 0.56 An advantage of vapply is that it stops in its tracks if FUN returns an unexpected value. sapply() and simplify2array() will silently give you an unexpected result (a single column matrix of mode list instead of a vector of numbers) and matrix(unlist()...) gives you a warning if you are lucky. > pBad <- p ; pBad[[length(pBad)/2]] <- 666 > system.time(zBad1 <- t(sapply(pBad,function(x)x))) user system elapsed 1.75 0.00 1.75 > zBad1[,499999:500001] # not what we wanted [[1]] [1] 499999.00000 18.93157 [[2]] [1] 666 [[3]] [1] 500001.00000 18.93157 > system.time(zBad2 <- t(simplify2array(pBad))) user system elapsed 0.5 0.0 0.5 > system.time(zBad3 <- matrix(unlist(pBad), ncol=2, byrow=TRUE)) user system elapsed 0.03 0.00 0.03 Warning message: In matrix(unlist(pBad), ncol = 2, byrow = TRUE) : data length [1999999] is not a sub-multiple or multiple of the number of rows [1000000] > # no warning if length(unlist(p)) were even > system.time(zBad4 <- t(vapply(pBad,function(x)x,numeric(2)))) Error in vapply(pBad, function(x) x, numeric(2)) : values must be length 2, but FUN(X[[500000]]) result is length 1 Timing stopped at: 0.29 0 0.28 Which of the latter two methods you choose depends on how likely errors in the data are. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf > Of R. Michael Weylandt > Sent: Tuesday, December 04, 2012 2:59 PM > To: arun > Cc: R help; s...@gnu.org > Subject: Re: [R] list to matrix? > > On Tue, Dec 4, 2012 at 8:17 PM, arun <smartpink...@yahoo.com> wrote: > > Hi, > > Try this: > > list1<-list(c(50000, 101), c(1e+05, 46), c(150000, 31), c(2e+05, 17), > > c(250000, 19), c(3e+05, 11), c(350000, 12), c(4e+05, 25), > > c(450000, 19), c(5e+05, 16)) > > > > > > res<-t(sapply(list1,function(x) x)) > > Bah Humbug! (In Christmas cheer) > > No need for all this (see solutions including mine already given) -- > but even without those, this is silly. An identity map is a real waste > if you just want the simplification bit of sapply() -- you'd be much > better just using simplify2array() > > Michael > > ______________________________________________ > 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.
