R/get_main_frequency.R

In earthtide: Parallel Implementation of 'ETERNA 3.40' for Prediction and Analysis of Earth Tides

#' get_main_frequency
#'
#' Get the frequency of the wave with the maximum amplitude in a range.
#'
#' @param start the starting frequency in cycles per day (numeric)
#' @param end the ending frequency in cycles per day (numeric)
#'
#' @return the main frequency between start and end
#' @export
#'
get_main_frequency <- function(start, end) {
  if (length(start) != length(end)) {
    stop("start and end must be the same length")
  }

  if (any(start > end)) {
    stop("all values of start must be greater than the corresponding values of
         end")
  }

  mn <- c()
  for (i in seq_along(start)) {
    inds <- ksm04$frequency_cpd >= start[i] & ksm04$frequency_cpd < end[i]
    et_sub <- ksm04[inds, ]
    mn[i] <- et_sub[which.max(et_sub$amplitude), "frequency_cpd"]
  }

  return(mn)
}