R/getInterval.R

In jstaf/actmon: A tool for parsing output produced by TriKinetics' Drosophila Activity Monitor.

#' Determine measurement interval
#' 
#' This method calculates the time difference between measurements in your
#' dataset.
#' 
#' @param obj A valid DAM S4 object.
#'   
#' @return Time interval between measurements in seconds.
#' @export
#' 
#' @examples
#' getInterval(DAM_DD)
setGeneric("getInterval", function(obj) {standardGeneric("getInterval")})
setMethod("getInterval", signature = "DAM",
          definition = function(obj) {
            if (length(obj@data[, 1]) <= 1) {
              stop("Interval cannot be calculated if there are less than two datapoints.")
            } else {
              # remove nas
              temp <- na.omit(obj@data)
              idxDiff <- temp[2, 1] - temp[1, 1]
              if (is.na(idxDiff) || (idxDiff < 1)) {
                stop("Something is wrong with the first few read indices of your data.")
              }
              
              return(as.numeric(difftime(temp[2, 2], temp[1, 2], units = "secs")) / idxDiff)
            }
          })