
library(testthat)

source("user_code.R")
test_that("returns a data frame sorted by Department in ascending order", {
  df <- data.frame(
    Name = c("Alice", "Bob", "Charlie", "Diana", "Eve"),
    Department = c("IT", "HR", "IT", "HR", "IT"),
    Salary = c(70000, 60000, 80000, 75000, 60000),
    stringsAsFactors = FALSE
  )
  res <- sort_by_multiple_columns(df)
  expect_true(is.data.frame(res), "Result should be a data frame.")
  expect_equal(res$Department, c("HR", "HR", "IT", "IT", "IT"),
               info = "Departments should be sorted ascending.")
})

test_that("within each Department, sorts by Salary in ascending order", {
  df <- data.frame(
    Name = c("A", "B", "C", "D", "E", "F"),
    Department = c("HR", "HR", "IT", "IT", "HR", "IT"),
    Salary = c(80000, 60000, 75000, 60000, 75000, 80000),
    stringsAsFactors = FALSE
  )
  res <- sort_by_multiple_columns(df)
  hr_salaries <- res$Salary[res$Department == "HR"]
  it_salaries <- res$Salary[res$Department == "IT"]
  expect_equal(hr_salaries, sort(hr_salaries),
               info = "HR salaries should be sorted ascending.")
  expect_equal(it_salaries, sort(it_salaries),
               info = "IT salaries should be sorted ascending.")
})

test_that("does not modify the original data frame", {
  df <- data.frame(
    Name = c("Alice", "Bob", "Charlie"),
    Department = c("IT", "HR", "IT"),
    Salary = c(70000, 60000, 80000),
    stringsAsFactors = FALSE
  )
  df_copy <- df
  sort_by_multiple_columns(df)
  expect_equal(df, df_copy, info = "Original data frame must not be modified.")
})

test_that("handles multiple departments and duplicate salary values correctly", {
  df <- data.frame(
    Name = c("A", "B", "C", "D", "E", "F"),
    Department = c("HR", "HR", "IT", "IT", "HR", "IT"),
    Salary = c(60000, 60000, 80000, 60000, 60000, 80000),
    stringsAsFactors = FALSE
  )
  res <- sort_by_multiple_columns(df)
  # All HR rows first, then IT
  expect_true(all(res$Department[1:3] == "HR"), "First three should be HR.")
  expect_true(all(res$Department[4:6] == "IT"), "Last three should be IT.")
  # Within HR, salaries must be sorted (even if duplicates)
  hr_salaries <- res$Salary[res$Department == "HR"]
  expect_equal(hr_salaries, sort(hr_salaries),
               info = "HR salaries with duplicates should be sorted ascending.")
})

test_main.R

Master the essential R data structures used in exploratory data analysis (EDA), focusing on practical applications and hands-on challenges. This course is designed for learners already familiar with R syntax, core data structures, and data cleaning/wrangling techniques.

Explore the essential R data structures that power effective exploratory data analysis, with a focus on practical usage and hands-on challenges.

Challenge: Sorting and Ordering

Solution