mapply is still a (disguised) loop (at the interpreted level). So other than improving code readability (always a good thing!), it shouldn't make much of an efficiency difference.
A longer answer is: if all you're doing is a location-scale family of distributions, then creating a matrix of standard normal (or whatever) distributed data for all 1:N at once and then using matrix operations to multiply and add, say, so each column becomes your different distribution might be faster. This gets the loops down to C code. A shorter answer is: it's unlikely that any of this makes enough of a difference to be worth the effort. Random number generation is so efficient in R that "avoiding loops" rarely matters. Also see ?replicate for a way to perhaps write cleaner code (but still using hidden interpreted loops). -- Bert Gunter -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Christos Hatzis Sent: Thursday, October 16, 2008 1:06 PM To: 'David Afshartous'; r-help@r-project.org Subject: Re: [R] Loop avoidance in simulating a vector Have a look at mapply. -Christos > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of David Afshartous > Sent: Thursday, October 16, 2008 3:47 PM > To: r-help@r-project.org > Subject: [R] Loop avoidance in simulating a vector > > > > All, > > I'd like to simulate a vector that is formed from many > distinct distributions and avoid a loop if possible. E.g, consider: > > mu = c(1, 2, 3) > sigma = c(1, 2, 3) > n = c(10, 10, 10) > > And we simulate a vector of length 30 that consists of > N(mu[i], sigma[i]) > distributed data, each of length n[i]. Of course for just > three groups we > can simply write it out as: > > DV = c(rnorm(n[1], mu[1], sigma[1]), rnorm(n[2], mu[2], > sigma[2]), rnorm(n[3], mu[3], sigma[3]) ) > > For many groups we can use a loop (assuming equal numbers per group): > > n = n[1] > DV = numeric(N*n) > for (i in 1:N) { > DV[(n*i - (n-1)): (n*i)] = rnorm(n, mu[i], sigma[i]) > } > > Is there any way to do the general cas without using a loop? > > Cheers, > David > > ______________________________________________ > 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. ______________________________________________ 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.
