write a code to identify states in timeseries data with hmm in r

Here is an example code for identifying states in timeseries data using Hidden Markov Models in R.

main.r
library(HMM)

# create a simulated timeseries data with 3 states
set.seed(123)
n <- 100
x <- c(rnorm(n/3, mean=0, sd=1), rnorm(n/3, mean=2, sd=1), rnorm(n/3, mean=-2, sd=1))

# define number of states
n_states <- 3

# build HMM model
hmm_model <- initHMM(c("state1", "state2", "state3"), c("A", "B"), transProbs=matrix(c(.6, .2, .2, .2, .6, .2, .2, .2, .6), n_states, n_states))

# normalize the observation data
norm_x <- (x - mean(x))/sd(x)

# fit HMM model to normalized data
fit <- BaumWelch(norm_x, hmm_model$hmm)

# Viterbi algorithm to identify states
viterbi_path <- viterbi(norm_x, hmm_model$hmm)

# plot original data with identified states
plot(x, type="l", main="HMM State Identification")
for (i in 1:(length(viterbi_path)-1)) {
  lines(c(i, i+1), c(x[i], x[i+1]), col=viterbi_path[i])
}
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The above code assumes that the timeseries data is stored in a vector x. We first create a simulated data with 3 different states. We then define the number of states we want to identify and build an HMM model with transition probabilities between the states. We normalize the observation data and fit the HMM model using the Baum-Welch algorithm. Finally, we apply the Viterbi algorithm to the normalized data, which assigns the most likely state to each observation. We plot the original data with the identified states.

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