3  Programming with functions

3.1 ⭐️ Overview

The basic question I asked while developing tabler was how do you pass a function as an argument to another function.

This chapter still needs a lot of work.

3.2 🌎 Useful websites

• Advanced R: Functionals

3.3 📦 Load packages

library(dplyr, warn.conflicts = FALSE)

3.4 🔢 Simulate data

Here we simulate a small data set that is intended to be representative of data from a research study.

set.seed(123)
study <- tibble(
  id     = as.character(seq(1001, 1020, 1)),
  sex    = factor(sample(c("Female", "Male"), 20, TRUE)),
  date   = sample(seq.Date(as.Date("2021-09-15"), as.Date("2021-10-26"), "day"), 20, TRUE),
  days   = sample(1L:21L, 20L, TRUE),
  height = rnorm(20, 71, 10)
)

# Add missing values for testing
study$id[3] <- NA
study$sex[4] <- NA
study$date[5] <- NA
study$days[6] <- NA
study$height[7] <- NA

3.5 Examples

This needs to be cleaned up. I’m just in a rush.

# Function passed to a function?
fn_number <- function(x) {
  x
}

fn_number(3)

[1] 3

fn_sum <- function(n, fn) {
  1 + fn(n)
}

fn_sum(3, fn_number)

[1] 4

lapply2 <- function(x, f, ...) {
  out <- vector("list", length(x))
  for (i in seq_along(x)) {
    out[[i]] <- f(x[[i]], ...)
  }
  out
}

lapply2(select(study, days, height), mean)

[[1]]
[1] NA

[[2]]
[1] NA

lapply2(select(study, days, height), mean, na.rm = TRUE)

[[1]]
[1] 12.05263

[[2]]
[1] 72.33294

# How do I make this work like purrr, dplyr, etc.
lapply2(select(study, days, height), ~ mean(.x, na.rm = TRUE))

Error in f(x[[i]], ...): could not find function "f"