從函式回傳值

R 函式撰寫入門

Richie Cotton

Data Evangelist at DataCamp

簡單加總函式

simple_sum <- function(x) {

  if(anyNA(x)) {

    return(NA)

  }

  total <- 0
  for(value in x) {
    total <- total + value
  }
  total
}

simple_sum(c(0, 1, 3, 6, NA, 7))

NA

再談幾何平均數

calc_geometric_mean <- function(x, na.rm = FALSE) {
  assert_is_numeric(x)
  if(any(is_non_positive(x), na.rm = TRUE)) {
    stop("x contains non-positive values, so the geometric mean makes no sense.")
  }
  na.rm <- coerce_to(use_first(na.rm), "logical")
  x %>%
    log() %>%
    mean(na.rm = na.rm) %>%
    exp()
}

回傳 NaN 並顯示警告

calc_geometric_mean <- function(x, na.rm = FALSE) {
  assert_is_numeric(x)
  if(any(is_non_positive(x), na.rm = TRUE)) {

    warning("x contains non-positive values, so the geometric mean makes no sense.")
    return(NaN)

  }
  na.rm <- coerce_to(use_first(na.rm), "logical")
  x %>%
    log() %>%
    mean(na.rm = na.rm) %>%
    exp()
}

提早回傳的原因

你已經知道答案。
輸入屬於邊界情況。

隱藏回傳值

simple_sum <- function(x) {
  if(anyNA(x)) {
    return(NA)
  }
  total <- 0
  for(value in x) {
    total <- total + value
  }
  total
}

simple_sum(c(0, 1, 3, 6, 2, 7))

隱藏回傳值

simple_sum <- function(x) {
  if(anyNA(x)) {
    return(NA)
  }
  total <- 0
  for(value in x) {
    total <- total + value
  }

  invisible(total)

}

simple_sum(c(0, 1, 3, 6, 2, 7))

許多圖會隱性回傳物件

ggplot(snake_river_visits, aes(n_visits)) +
  geom_histogram(binwidth = 10)

Snake River 造訪次數的長條圖。分佈右偏，多數人在每年不到 5 次的左側區間；最大值超過每年 300 次。

許多圖會隱性回傳物件

srv_hist <- ggplot(snake_river_visits, aes(n_visits)) +
  geom_histogram(binwidth = 10)

str(srv_hist, max.level = 0)

List of 9
 - attr(*, "class")= chr [1:2] "gg" "ggplot"

與前一張投影片相同的 Snake River 造訪次數長條圖。

一起來練習吧！

R 函式撰寫入門