Anonymous Functions

Schwab

Digression

Anonymous functions are functions without a name.

A named function

library(stringr)

#This function has a name, upper_case

upper_case <-  function(word){
  str_to_upper(word)
}

upper_case("hi")

[1] "HI"

Anonymous functions

This is the same function without a name

function(word) str_to_upper(word)

function(word) str_to_upper(word)

Its harder to use by itself, we often use them in combination with other functions.

Using the anonymous function

The function after .f will only be used once, we don’t need to name it.

words <- c("I", "Like", "to", "eat", "cheese", "!")
purrr::map_chr(
  .x = words,
  .f = function(word) str_to_upper(word)
)

[1] "I"      "LIKE"   "TO"     "EAT"    "CHEESE" "!"

Name an anonymous function

You can name an anonymous function.

# This works with map_chhr() because str_to_upper is vectorized

upper_case_anon <- function(word) str_to_upper(word)
upper_case_anon(words)

[1] "I"      "LIKE"   "TO"     "EAT"    "CHEESE" "!"

Does this work?

# This works because str_to_upper is vectorized

upper_case_anon <- function(word) 
  str_to_upper(word)

upper_case_anon(words)

[1] "I"      "LIKE"   "TO"     "EAT"    "CHEESE" "!"

Yes, but it can get confusing.

This does not work

library(tidyverse)

confusing_function <- function(word) 
  upper_case_words<- 
    str_to_upper(word)
## This should lower the word's case, but it doesn't because its not part of the function.  
  str_to_lower(upper_case_words)

confusing_function(words)

Last example fixed with

confusing_function <- function(word){ 
  upper_case_words<- 
    str_to_upper(word)
  ## Now it is part of the function.  
  str_to_lower(upper_case_words)
}
  
confusing_function(words)

[1] "i"      "like"   "to"     "eat"    "cheese" "!"

Summary

Use an anonymous function to do one thing.

If it get complicated give some {}

More anonymous?

Since R version 4.1, May 2021.

Just use a \(argument) operations

# This is also an anonymous function. 
\(word) str_to_upper(word)

map_chr(.x = words,
    .f = \(word) str_to_upper(word))

Deep dive

There are actually lots of ways of making anonymous functions.

Here are more. I like the idea of the lambda package.