
library(testthat)

source("user_code.R")
test_that("trim_whitespace removes leading and trailing whitespace", {
  input <- c("  apple ", "banana", "  cherry  ", "   ", "grape")
  expected <- c("apple", "banana", "cherry", "", "grape")
  result <- trim_whitespace(input)
  expect_equal(result, expected, info = "trim_whitespace should remove all leading and trailing spaces from each string")
})

test_that("to_lowercase converts all characters to lowercase", {
  input <- c("Apple", "BANANA", "Cherry", "123", " ")
  expected <- c("apple", "banana", "cherry", "123", " ")
  result <- to_lowercase(input)
  expect_equal(result, expected, info = "to_lowercase should convert all letters to lowercase and leave non-letter characters unchanged")
})

test_that("clean_strings applies both trimming and lowercasing", {
  input <- c("  Hello ", "WORLD  ", " R Programming  ", "   ", "123ABC  ")
  expected <- c("hello", "world", "r programming", "", "123abc")
  result <- clean_strings(input)
  expect_equal(result, expected, info = "clean_strings should trim whitespace and convert to lowercase for each string")
})

test_that("functions handle strings with only whitespace or no whitespace", {
  input <- c("   ", "NOCHANGE", "all lower", "  MIXED Case  ")
  trimmed_expected <- c("", "NOCHANGE", "all lower", "MIXED Case")
  lower_expected <- c("   ", "nochange", "all lower", "  mixed case  ")
  clean_expected <- c("", "nochange", "all lower", "mixed case")
  expect_equal(trim_whitespace(input), trimmed_expected, info = "trim_whitespace should handle strings with only whitespace and no whitespace")
  expect_equal(to_lowercase(input), lower_expected, info = "to_lowercase should handle strings with only whitespace and no whitespace")
  expect_equal(clean_strings(input), clean_expected, info = "clean_strings should handle all edge cases")
})

test_main.R

The `gsub("^\\s+|\\s+$", "", x)` command uses regular expressions to clean up strings:

- `^\\s+` matches one or more whitespace characters at the start of a string;
- `|` means 'or';
- `\\s+$` matches one or more whitespace characters at the end of a string.

`gsub` replaces all matches of these patterns with an empty string (`""`), effectively removing all leading and trailing spaces from each element in the vector `x`. This leaves only the inner content of each string untouched.

Definition

Master the art of writing and using functions in R, from basic syntax to advanced functional programming techniques. This course guides you through creating your own functions, leveraging anonymous functions, and applying functional programming concepts to solve real-world problems in R.

Learn how to define, call, and utilize functions in R, including understanding parameters, return values, and default arguments.

Discover how to use anonymous (inline) functions for concise, on-the-fly operations, and see how they fit into R's functional programming paradigm.

Apply functional programming concepts in R to solve real-world problems, focusing on writing concise, reusable, and efficient code.

Challenge: Compose Your Own Functions

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