Death and birth process and proportion - r

Question

I have this code which describes a death and birht procceses with four states, 0,1,2,3.
bd_process <- function(lambda, mu, initial_state = 0, steps = 100) {
time_now <- 0
state_now <- initial_state
time <- 0
state <- initial_state
for (i in 1:steps) {
if (state_now == 3) {
lambda_now <- 0
} else {
lambda_now <- lambda
}
if (state_now == 0) {
mu_now <- 0
} else {
mu_now <- mu
}
time_to_transition <- rexp(1, mu_now + lambda_now)
if (runif(1) < mu_now/(lambda_now + mu_now)) {
state_now <- state_now - 1
} else {
state_now <- state_now + 1
}
time_now <- time_now + time_to_transition
time <- c(time, time_now)
state <- c(state, state_now)
}
return(list(time = time, state= state))
}
From this code I want to create a function which count the proportion of time in each time. The function is aimed to take two parameters, and Im a bit lost. Any suggestions?

Answer 1

This is an example function that identifies the times for each state and sums them. It uses sapply to iterate over the possible states.
x=bd_process(2,3)
#' #param x a list returned by bd_process function
#' #return a vector of times spent in state 0,1,2,3
get_times=function(x) {
sapply(0:3, function(i) {
sum(x$time[which(x$state==i)])
})
}
get_times(x)
[1] 401.52405 607.44447 253.52741 38.58117