R/interlace.R

In Sumpfohreule/MyUtilities: Collection of general functions which are useful in multiple contexts

#' Combine two vectors in alternating order
#'
#' A new vector is created which contains the values of both input vectors in
#' alternating order beginning with the first input vector
#'
#' @param vector_1,vector_2 Any vector which is compatible with the other or
#' coercible
#' @export
#'
interlace <- function(vector_1, vector_2) {
  if (is.null(vector_1)) {
    return(vector_2)
  } else if (is.null(vector_2)) {
    return(vector_1)
  }

  v1_len <- length(vector_1)
  v2_len <- length(vector_2)
  min_length <- min(v1_len, v2_len)
  i <- 0:(min_length * 2 - 1)

  index_sequence <- (i %% 2) * v1_len + (i %/% 2) + 1
  out_vector <- c(vector_1, vector_2)[index_sequence]

  if (v1_len > v2_len) {
    add_index <- (min_length + 1):v1_len
    out_vector <- c(out_vector, vector_1[add_index])
  } else if (v2_len > v1_len) {
    add_index <- (min_length + 1):v2_len
    out_vector <- c(out_vector, vector_2[add_index])
  }
  return(out_vector)
}