A couple days ago, Mark Leeds asked about a solution that would
basically stagger two lists, a and b, to return a list in the form of
a[1], b[1], a[2], b[2], a[3].... In particular, the summary of his
question was in reference to lists defined by
x <- 5
tempin <- seq(1,1411, by=30)
a <- tempin
b <- tempin + x
I offered the following function
everyOther <- function(tempin, x){
tempout <- array(data=NA, dim=length(tempin)*2)
tempout[seq(1,length(tempin)*2, by=2)]<-tempin
tempout[seq(2,length(tempin)*2, by=2)]<-tempin+x
tempout
}
which did what it was supposed to, and Gavin Simpson offered a
similar function. Peter Dalgaard, however, supplied a much more
elegant solution:
c(rbind(tempin,tempin+5))
or
rep(tempin, each=2) + c(0,5)
I thought I'd bring this up as a new topic because it's really no
longer related to what Mark first asked, but is there a way, perhaps
from the documentation, that a user would know that c() and lists in
general behave as they do in these two lines? Or would we just need
to dig into the code?
I am reminded of quote by Byron Ellis: "Contrary to popular belief
the speed of R's interpreter is rarely the limiting factor to R's
speed. People treating R like C is typically the limiting factor. You
have vector operations, USE THEM." Not exactly the point, but close.
Thanks!
Jeff Spies
http://www.nd.edu/~jspies/
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