[R] transitions in R

[Philippe Grosjean]

>Hi, All.  I'd have a set of data in an array:

>process <- c( 5 , 7 , 4 , 1 , 4 , 1 , 4 , 1 , 4 , 4 , 1 , 5 , 4 , ...)

>and I'd like to know the number of transitions in this data.  I
>calculate transitions as the number of times a number follows another
>number.  thus, something like this would be a 1 deep transition:

>1 --> 1 : 10% (and actual number of 1 --> 1 occurrences)
>1 --> 2 : 2%
>1 --> 3 : 23%
>...
>2 --> 1 : 2%
>2 --> 2 : 8%
>(etc.)

>of course, you can have 2 or 3 or n deep transitions, but I'm really
>only interested in 1 and 2 (and maybe 3) deep transitions.

>what is the best way of calculating this info in R?

>thanks!
>greg

transitions <- function(vect, t1, t2) {
  # vect is the vector to test
  # t1 is the vector of all initial states of the transitions
  # t2 is the vector of all final states of the transitions
  n <- length(vect)
  nt <- length(t1)   # rem: t2 must be same length, not tested here
  v <- rep(vect, nt)
  dim(v) <- c(n, nt)
  v <- t(v)
  tests <- (v[, 1:(n-1)]==t1 & v[, 2:n]==t2)
  res <- apply(tests, 1, "sum", na.rm=T)
  res
}

> p <- c(1,2,3,2,1,1,2,1,3)
> transitions(p, c(1,1,1,2,2,2), c(1,2,3,1,2,3))
[1] 1 2 1 2 0 1


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