On Wed, 24 Oct 2007, Johannes H?sing wrote:
Dear expeRts,
recently I asked for a nice way to re-program a problem
without using control constructs such as "for" or
"sapply(1:length(x), ...". Is there a way to program
a random walk with a reflecting boundary without resorting
to such constructs? A working solution is
ranwalk <- function(length, bound) {
k <- cumsum(sample(c(-1, 1), length, replace=TRUE))
while( any(abs(k) > bound) ) {
ri <- min(which(abs(k) > bound))
k[ri:length] <- k[ri:length] - 2 * sign(k[ri])
}
k
}
but it uses "while" and has the same expression in the
"while" statement and the following line. Is there
a sensible way to reprogram it using the "whole object"
approach?
Does this satisfy your 'sensible' sensibility?
ranwalk2 <-
function(length., bound) {
k <- cumsum(sample(c(-1, 1), length., replace=TRUE))
lk <- rep( c( 0:bound, (bound-1):(-bound), (1-bound):(-1)),
length=max(abs(k))+1)
sign(k)*lk[ 1 + abs(k) ]
}
HTH,
Chuck
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:[EMAIL PROTECTED] UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
