using <<- with a changing variable name (substitute?)
On Mon, 8 Aug 2005, Tamas K Papp wrote:
I have a matrix r and a scalar d, and I would like to apply the
following functions to each of its elements:
1. if r < 0, no change
2. if 0 <= r < d, replace element by zero
3. if d <= r, replace element by r-d
I wrote a small function for this
m <- function(b) {sapply(b, function(bb) {
if (bb < 0) {bb} else {if (bb>d) {bb-d} else 0}
})}
Why use sapply? r[] <- ifelse(r >= d, r-d, ifelse(r >= 0, 0, r)) is one more efficient way.
so I can simply say r <- m(r). The problem is that the matrix r is huge and only one of them fits in the memory,
If that is literally true, you cannot do this at R level AFAICS. The only way I can see that you can do this with standard semantics is m(r) <- d with a replacement function m<-() written using .Call. Using "m<-" <- function(r, d) ifelse(r >= d, r-d, ifelse(r >= 0, 0, r)) is going to make several copies.
and I don't need the original r, so I would like to do this memory-efficiently. Moreover, there are matrices with various names (not only r) so I need a generic function (they don't fit in memory at the same time, I load, save and rm them). I tried various combinations of <<-, assign, substitute etc. but could not get it working. Could somebody please help me?
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595