从函数返回值

R 函数编写入门

Richie Cotton

Data Evangelist at DataCamp

一个简单的求和函数

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

再谈几何平均数

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()
}

带警告返回 NaN

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()
}

提前返回的原因

你已知答案。
输入是边界情况。

隐藏返回值

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))

隐藏返回值

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))

许多图会隐式返回对象

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

Snake River 访问直方图。分布右偏，多数人在每年少于 5 次的最左侧柱中。最大值超过每年 300 次。

许多图会隐式返回对象

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"

与上一页相同的 Snake River 访问直方图。

让我们练习！

R 函数编写入门