i'm not so sure i understood, but you might want something in the
lines of:
z <- outer(x, x, "-")
(abs(z)>step)*outer(1:length(x), 1:length(x))*z
(not tested)
b
On Jan 23, 2008, at 11:32 AM, papagenic wrote:
dear experts,
I am new to R and am trying to compute a vector y from a vector x
where :
y[i] = sign(x[j]-x[i])*(j-i) with j the first index after i where
abs(x[j]-x[i]) > to a given step
y[i] is 0 if there is no such j
I can write this in R as follows
for(i in 1:length(x)) {
y[i]=0
for(j in i:length(x)) {
if (abs(x[j]-x[i]) > step) {
y[i]=sign(x[j]-x[i])*(j-i)
break;
}
}
}
but I wonder if there is a more efficient way to write this. I
understand
explicit looping can often be avoided in R using vector notation.
Thanks for your help
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