R/helpers.R

In simonecollier/lizardHMM: Fitting Lizard Movement Data with HMMs

#' Split vector into list
#'
#' This function splits a vector from the index start to the index end into
#' segments of length length and complies them into a list. This function can
#' also apply the exponential function to the vector elements if desired.
#'
#' @param vector The vector to be split into a list.
#' @param start The first index of the vector vector that will be included in
#'   the list.
#' @param end The last index of the vector vector that will be included in the
#'   list.
#' @param length A value indicating the length of the segments that vector
#'   will be split into.
#' @param exp A logical variable indicating whether the elements of vector
#'   should be transformed with `exp()`.
#'
#' @return A list of the sections of the split vector.
#' @export
#' @examples
#' split_vec(c(1, 2, 3, 4, 5, 6, 7, 8, 9), 3, 6, 2)
#' split_vec(c(0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6), 2, 7, 3, exp = TRUE)

split_vec <- function(vector, start, end, length, exp = FALSE, tanh = FALSE) {
  if (exp) {
    return(split(exp(vector[start:end]),
                 ceiling(seq_along(exp(vector[start:end]))/length)))
  }
  if (tanh) {
    return(split((tanh(vector[start:end]) + 1)/2,
                 ceiling(seq_along((tanh(vector[start:end]) + 1)/2)/length)))
  }
  split(vector[start:end], ceiling(seq_along(vector[start:end])/length))
}

#' Compute Euclidean distance
#'
#' This function computes the euclidean distance between two vectors of
#' coordinates.
#'
#' @param x_positions A vector of positions along the x-axis.
#' @param y_positions A vector of positions along the y-axis.
#'
#' @return A vector of euclidean distances.
#' @export
euclidean_distance <- function(x_positions, y_positions) {
  x_distances <- diff(x_positions)
  y_distances <- diff(y_positions)
  euclidean   <- numeric()
  for (i in 1:length(x_distances)) {
    euclidean[i] <- sqrt(x_distances[i]^2 + y_distances[i]^2)
  }
  euclidean
}