I have spent over a day trying to accomplish what seems to be a very simple thing. I have to create 300 'random' sequences in which the numbers 1,2,3 and 4 all appear exactly 12 times, but the same number is never used twice 'in a row'/consecutively.
My best attempts (I guess) were:
have R sample 48 items without replacement, test whether there are consecutive values with rle, then use only the sequences that do not contain consecutive values. Problem: there are almost no random sequences that meet this criterion, so it takes forever.
have R create sequences without consecutive values (see code).
pop<-rep(1:4,12)
y=c()
while(length(y)!=48)
{
y= c(y,sample(pop,48-length(y),replace=F))
y=y[!c(FALSE, diff(y) == 0)]
}
Problem: this creates sequences with varying numbers of each value. I then tried to use only those sequences with exactly 12 of each value, but that only brought me back to problem 1: takes forever.
There must be some easy way to do this, right? Any help is greatly appreciated!
Maybe using replicate() with a repeat loop is faster. here an example with 3 sequences. Looks like this would take approx. 1490 seconds with 300 (not tested).
set.seed(42)
seqc <- rep(1:4, each=12) # starting sequence
system.time(
res <- replicate(3, {
repeat {
seqcs <- sample(seqc, 48, replace=FALSE)
if (!any(diff(seqcs) == 0)) break
}
seqcs
})
)
# user system elapsed
# 14.88 0.00 14.90
res[1:10, ]
# [,1] [,2] [,3]
# [1,] 4 2 3
# [2,] 1 1 4
# [3,] 3 2 1
# [4,] 1 1 4
# [5,] 2 3 1
# [6,] 4 1 2
# [7,] 3 4 4
# [8,] 2 1 1
# [9,] 3 4 4
# [10,] 4 3 2