Returning values from functions

Introduction to Writing Functions in R

Richie Cotton

Data Evangelist at DataCamp

A simple sum function

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
Introduction to Writing Functions in R

Geometrics means again

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()
}
Introduction to Writing Functions in R

Returning NaN with a warning

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()
}
Introduction to Writing Functions in R

Reasons for returning early

  1. You already know the answer.
  2. The input is an edge case.
Introduction to Writing Functions in R

Hiding the return value

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))

19
Introduction to Writing Functions in R

Hiding the return value

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))
Introduction to Writing Functions in R

Many plots invisibly return things

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

A histogram of visits to Snake River. The distribution is right-skewed, with most people in the left-hand bar of under 5 visits per year. The largest value is over 300 visits per year.

Introduction to Writing Functions in R

Many plots invisibly return things

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"

The same histogram of Snake River visits from the previous slide is shown again.

Introduction to Writing Functions in R

Let's practice!

Introduction to Writing Functions in R

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