r - 从泛型函数创建新方法会在 R 中产生错误

Question

我正在 R 工作室写一个包。我创建了一个函数，它将创建一个类“mytrack”的对象，然后从现有的泛型中定义了几个方法，并在下面的代码中定义了一个具有新泛型的新方法。使用此构造函数创建的新对象将属于“mytrack”类，并将保存一些元数据以及点的坐标，这些点共同组成一条线。函数“distance2”将根据坐标计算这条线的长度。我的整个程序包以及计算距离的功能。问题是当我做 check() 时我得到 1 个便条。注意在代码之后。我的问题如下：

1. 怎么了？
2. 我如何解决它？

#' Constructor for object of a type "mytrack"
#'
#' @param name Name of the track
#' @param time Timestamps for points
#' @param crs CRS code
#' @param coordinates LON-LAT coordinates
#'
#' @return Object of a class "mytrack
#' @export
#'
#' @examples
#' \dontrun{
#' obj1 <- storetracks3("Track1", my_timestamps, 4326, my_coordinates)
#' }
storetracks3 <- function(name,time,crs,coordinates) {
  value <- list(my_name = name, my_time = time, my_crs = crs, my_coords=coordinates)
  attr(value, "class") <- "mytrack"
  value
}


#' Print method for class "mytrack"
#'
#' @param x object of a class "mytrack"
#' @param ... further arguments passed to or from other methods.
#'
#' @return Prints elements of object of a class "mytrack"
#' @export
#'
#' @examples
#' \dontrun{
#' print(obj1)}
print.mytrack <- function(x, ...) {
  cat("Name of this object is",x$my_name, "\n")
  cat("Timestamps are ", x$my_time, "\n")
  cat("CRS used is ", x$my_crs, "\n")
  print(x$my_coords)
}


#' Summary method for class "mytrack"
#'
#' @param object object of a class "mytrack"
#' @param ... further arguments passed to or from other methods.
#'
#' @return Prints summary of objects of a class "mytrack"
#' @export
#'
#' @examples
#' \dontrun{
#' summary(obj1)}
summary.mytrack <- function(object, ...) {
cat("Object has ", nrow(object$my_coords), " coordinates." )
}


#' Plot method for class "mytrack"
#'
#' @param x Object of a class "mytrack"
#' @param y Not used
#' @param ... Not used
#'
#' @return Plot in Cartesian xy system where Longitude is plotted on x and
#' latitude is plotted on y
#' @export
#'
#' @examples
#' \dontrun{
#' plot(obj1)}
plot.mytrack <- function(x,y, ...) {
  plot(x$my_coords,type="l")
}

#' Generic distance function
#'
#' @param obj Object of class "mytrack"
#' @param status TRUE for using S2 for distance calculation, or FALSE for not using it
#'
#' @return Distance in meters
#' @export
#'
distance2 <- function(obj,status) {
  UseMethod("distance2")
}

#' Distance method for "mytrack" class objects
#'
#' @param obj Object of class "mytrack"
#' @param status TRUE for using S2 for distance calculation, or FALSE for not using it
#'
#' @return Distance in meters
#'
#' @export
#' @import sf
#' @examples
#' \dontrun{
#' distance2.mytrack(obj1,TRUE)
#' }
distance2.mytrack <- function(obj,status) {
  sf::sf_use_s2(status)
  points <- list()
  for(row in 1:nrow(obj$my_coords)) {
    point <- sf::st_point(c(obj$my_coords[c(row),c(1)],obj$my_coords[c(row),c(2)]))
    points[[row]] <- point
  }
  sfc_object <- sf::st_sfc(points, crs=obj$my_crs)
  sf_object <- sf::st_sf(geom=sfc_object)
  points.nested <- sf_object %>% tidyr::nest(data=geom)
  to_line <- function(tr) sf::st_cast(sf::st_combine(tr), "LINESTRING") %>% .[[1]]
  (tracks <- points.nested %>% dplyr::pull(data) %>% purrr::map(to_line) %>% sf::st_sfc(crs = obj$my_crs))
  return(as.integer(sf::st_length(tracks)))
}

注意我得到：

 distance2.mytrack: no visible binding for global variable ‘geom’
 distance2.mytrack : to_line: no visible binding for global variable ‘.’
 distance2.mytrack: no visible binding for global variable ‘data’
 Undefined global functions or variables:
    . data geom
 Consider adding
    importFrom("utils", "data")
  to your NAMESPACE file.

感谢你的帮助。如有必要，我可以提供更多信息。

标签： rdataframe