I have a character string for which I want to store all possible windows of a given size. In my first approach I have done the following to accomplish this:
teststring<-c("ABCBDBDBCBABABD")
n <- nchar(teststring)
k <- 9
test = substring(teststring, 1:(n-k+1), k:n)
test1 = strsplit(test,"")
test2 = do.call(cbind, test1)
But I was wondering whether there is a better way to do it? I would also need to find a way to do this in a cyclical manner, i.e.:
A B C B D B D B C B A B A etc.
B C B D B D B C B A B A B
C B D B D B C B A B A B D
B D B D B C B A B A B D A
D B D B C B A B A B D A B
B D B C B A B A B D A B C
D B C B A B A B D A B C B
B C B A B A B D A B C B D
C B A B A B D A B C B D B
The following does not work, as is outlined in the documentation for substring:
test = substring(teststring, 1:n, c(k:n, 1:k))
Any help would be appreciated.
答案 0 :(得分：2)
For cyclical, I'd just paste your test-string together. Then substring is easy:
t2 = paste0(teststring, teststring)
substring(text = t2, 1:n, last = (1:n) + k)
# [1] "ABCBDBDBCB" "BCBDBDBCBA" "CBDBDBCBAB" "BDBDBCBABA" "DBDBCBABAB" "BDBCBABABD" "DBCBABABDA"
# [8] "BCBABABDAB" "CBABABDABC" "BABABDABCB" "ABABDABCBD" "BABDABCBDB" "ABDABCBDBD" "BDABCBDBDB"
# [15] "DABCBDBDBC"
If you'd prefer it in a matrix, you can always strsplit after, as akrun suggested in comments.
答案 1 :(得分：2)
If you need to create windows of sequence as matrices
v1 <- strsplit(teststring,'')[[1]]
ln <- length(v1)
m1 <- embed(c(v1,v1), ln)
m1[,ncol(m1):1]
Or
matrix(v1, nrow=ln+1, ncol=ln)[-(ln+1),]