Sorting By Functions in R Programming Language

Sometimes we’ll want to sort a collection by something other than its natural order. For example, suppose we wanted to sort strings by their length instead of alphabetically. Here’s an example of custom sorts in R.

library(dplyr)

main <- function() {
  fruits <- c("peach", "banana", "kiwi")

  # We implement a comparison function for string lengths
  len_cmp <- function(a, b) {
    nchar(a) - nchar(b)
  }

  # Now we can use this custom comparison function to sort fruits by name length
  sorted_fruits <- fruits[order(sapply(fruits, nchar))]
  print(sorted_fruits)

  # We can use the same technique to sort a list of values that aren't built-in types
  Person <- function(name, age) {
    list(name = name, age = age)
  }

  people <- list(
    Person("Jax", 37),
    Person("TJ", 25),
    Person("Alex", 72)
  )

  # Sort people by age
  sorted_people <- people[order(sapply(people, function(p) p$age))]
  print(sorted_people)
}

main()

In this R code:

1. We use the dplyr library for some convenient functions.

2. Instead of slices.SortFunc, we use R’s order function combined with sapply to sort our collections.

3. For the Person struct, we use a list in R as it’s the closest equivalent.

4. The sorting of complex types (like our Person list) is done using a similar approach as with the strings, but we access the age field of each person in the comparison function.

When you run this code, you should see output similar to:

[1] "kiwi"   "peach"  "banana"
[[1]]
[[1]]$name
[1] "TJ"
[[1]]$age
[1] 25

[[2]]
[[2]]$name
[1] "Jax"
[[2]]$age
[1] 37

[[3]]
[[3]]$name
[1] "Alex"
[[3]]$age
[1] 72

This demonstrates how to implement custom sorting in R, both for simple types like strings and for more complex custom types.