On Apr 29, 2010, at 1:58 PM, YasirKaheil wrote:
Hi,
I have a matrix of X and Y coordinates, and one pair of coordinates
that I
need to know it corresponds (or is closest) to which row in the
matrix. For
example:
MC<- cbind(rep(1:1000,each=1000),rep(1:1000,1000));
p<-c(543.1,440.05);
I know that if you do which.min you'll get the answer, which will be
row #
542440, but which.min is slow and this process needs to be repeated
a lot.
It didn't seem to be particularly slow when I tried it:
> which.min( abs(MC[,1]-p[1])+ abs(MC[,2]-p[2]) ) # L1 metric
[1] 542440
system.time( which.min(abs(MC[,1]-p[1])+ abs(MC[,2]-p[2])) )
user system elapsed
0.068 0.034 0.103
What was your code and experience with it?
I tried using match and findInterval and %in% but I don't know how I
can use
them to find in 2 columns simultanuously.
--
David Winsemius, MD
West Hartford, CT
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