These are the ways that occur to me. ## This produces a logical vector, which will get converted to a numeric ## vector the first time a number is assigned to it. That seems ## wasteful. x <- rep(NA, n) ## This does the conversion ahead of time but it's still creating a ## logical vector first, which seems wasteful. x <- as.numeric(rep(NA, n)) ## This avoids type conversion but still involves two assignments for ## each element in the vector. x <- numeric(n) x[] <- NA ## This seems reasonable. x <- rep(as.numeric(NA), n) Comments? Thanks, Rob
On Thu, Nov 26, 2009 at 10:03 AM, Rob Steele <freenx.10.robsteele at xoxy.net> wrote:> These are the ways that occur to me. > > ## This produces a logical vector, which will get converted to a numeric > ## vector the first time a number is assigned to it. ?That seems > ## wasteful. > x <- rep(NA, n) > > ## This does the conversion ahead of time but it's still creating a > ## logical vector first, which seems wasteful. > x <- as.numeric(rep(NA, n)) > > ## This avoids type conversion but still involves two assignments for > ## each element in the vector. > x <- numeric(n) > x[] <- NA > > ## This seems reasonable. > x <- rep(as.numeric(NA), n) > > Comments?My intuition would be to go with the third method (allocate a numeric vector then assign NA to its contents) but I haven't tested the different. In fact, it would be difficult to see differences in, for example, execution time unless n was very large. This brings up a different question which is, why do you want to consider this? Are you striving for readability, for speed, for low memory footprint, for "efficiency" in some other way? When we were programming in S on machines with 1 mips processors and a couple of megabytes of memory, such considerations were important. I'm not sure they are quite as important now.
You can try this also: rep(NA_integer_, 10) On Thu, Nov 26, 2009 at 2:03 PM, Rob Steele <freenx.10.robsteele at xoxy.net> wrote:> These are the ways that occur to me. > > ## This produces a logical vector, which will get converted to a numeric > ## vector the first time a number is assigned to it. ?That seems > ## wasteful. > x <- rep(NA, n) > > ## This does the conversion ahead of time but it's still creating a > ## logical vector first, which seems wasteful. > x <- as.numeric(rep(NA, n)) > > ## This avoids type conversion but still involves two assignments for > ## each element in the vector. > x <- numeric(n) > x[] <- NA > > ## This seems reasonable. > x <- rep(as.numeric(NA), n) > > Comments? > > Thanks, > Rob > > ______________________________________________ > R-help at 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. >-- Henrique Dallazuanna Curitiba-Paran?-Brasil 25? 25' 40" S 49? 16' 22" O
> -----Original Message----- > From: r-help-bounces at r-project.org > [mailto:r-help-bounces at r-project.org] On Behalf Of Rob Steele > Sent: Thursday, November 26, 2009 8:03 AM > To: r-help at stat.math.ethz.ch > Subject: [R] Best way to preallocate numeric NA array? > > These are the ways that occur to me. > > ## This produces a logical vector, which will get converted > to a numeric > ## vector the first time a number is assigned to it. That seems > ## wasteful. > x <- rep(NA, n) > > ## This does the conversion ahead of time but it's still creating a > ## logical vector first, which seems wasteful. > x <- as.numeric(rep(NA, n)) > > ## This avoids type conversion but still involves two assignments for > ## each element in the vector. > x <- numeric(n) > x[] <- NA > > ## This seems reasonable. > x <- rep(as.numeric(NA), n) > > Comments?I like the rep-based ones because they are more 'functional': I can pass the output directly into another function. If speed is a big concern, I think that x <- rep.int(NA_real_, n) may be the fastest but then it is not immediately apparent how to do the same for integer or fancier classes. (NA_real_ is to the numeric class as NA_integer_ is to the integer class.) Your last one, rep(as.<class>(NA), n), seems to me to be a good compromise between readability and speed. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com> > Thanks, > Rob > > ______________________________________________ > R-help at 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. >