# Re: [R] Infinite loop

From: Hosack, Michael <mhosack_at_state.pa.us>
Date: Tue, 22 Mar 2011 13:56:14 -0400

Thank you so much Martyn. Now I can most likely avoid having to rerun my program multiple times.

Mike

Hi,

This might do what you want:

pmove <- sample((1 - ss[i]):(40-ss[i]))
## drop all step sizes that puts the new value within 7 places of
the previous value

pmove <- pmove[abs(pmove)>7]
## calculate potential next values
pss <- pmove + ss[i]
## flag any values that are already in the sample
if (found) {

```      ## use the first value that is not already in the sample
} else {
## all potential values are already in the sample, so choose
another starting point
break
```

}
}
if (found) break
if (iter > 100) {
cat("Giving up\n")
break
}
}

It randomly chooses a starting value, then chooses the next value based on a randomly selected step size rather than directly. It keeps doing this until it either uses all possible values, or gets stuck in which case it randomly selects another starting value. If it can't find a solution in 100 goes it gives up.

Martyn

R experts,

Hello, I am trying to sample a vector 1:40 without replacement such that no element in the new vector
is within 7 units of either of its immediate neighbors. This is part of a larger program I am working
on. The following code works well about 65 % of the time (14/40). The problem I encounter happens when
the last element remaining to be sampled from the vector STRATA is within 7 digits +- of the last element
in the vector s1, at which point an infinite loop occurs. At least that's what I think is happening.
Any help would be greatly appreciated.

Thank you,

Mike

require(IRanges)
STRATA <- 1:40
s1 <- sample(STRATA, 1)
for (i in seq(from = 1, to = 39, by = 1)){   repeat{
tmp <- sample(STRATA, 1)

if (!any(s1 == tmp) & !any(as.vector(IRanges(s1[length(s1)]-7, s1[length(s1)]+7)) %in% tmp)) break

}
s1 <- c(s1,tmp)
}
s1

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