R Quiz

How it works

Answer before running: does vector arithmetic align names, does mode calculate the most frequent value, do factor codes reproduce numeric labels, and does one-column extraction always keep a data frame? Each question concerns an actual R behaviour that can make a plausible-looking result wrong.

Run this R example

These examples run locally with R, not PHP, Python or JavaScript. The reviewed baseline is R 4.5.2 on Windows x64/UCRT, using only packages shipped with R. This is a tested version, not a newest-release claim. Install your own R from the official R project; an IDE is optional. Save the complete source as quiz.R in a separate learning folder and run Rscript --vanilla quiz.R. Keep code and fictional fixtures separate from a real project.

Bhylu has no R browser runner. There is no Try in playground link because the existing Python and JavaScript editors do not execute R. No package installation, account, network dataset, Apache, MySQL or PHP setting is needed to run these base-R sources.

The complete download uses a local scope, restores its temporary options and treats unexpected warnings as errors. Examples that handle an expected warning do so narrowly. Random examples change only their R process’s RNG state. File examples own their temporary output; figure examples leave their named PNG in the current learning folder and refuse to overwrite it. Use a new empty folder to rerun a figure.

Download the complete quiz.R · Download all source files with hash checks

For the optional collection downloader, save download-examples.mjs in an empty folder and run node download-examples.mjs. Local preview before publishing uses node download-examples.mjs http://127.0.0.1:8000/examples/r/. It refuses an existing bhylu-r-examples folder and does not install or execute R.

Example

local({
  previous_options <- options(warn = 2, digits = 8, stringsAsFactors = FALSE)
  on.exit(options(previous_options), add = TRUE)
  answers <- c("Vector arithmetic aligns names" = FALSE,
    "mode computes statistical mode" = FALSE,
    "Factor codes are original numeric labels" = FALSE,
    "Single-column extraction always keeps a data frame" = FALSE)
  for (name in names(answers)) cat(name, ": ", answers[[name]], "\n", sep = "")
  invisible(NULL)
})

answers <- c("Vector arithmetic aligns names" = FALSE,
  "mode computes statistical mode" = FALSE,
  "Factor codes are original numeric labels" = FALSE,
  "Single-column extraction always keeps a data frame" = FALSE)
for (name in names(answers)) cat(name, ": ", answers[[name]], "\n", sep = "")

Expected result

Vector arithmetic aligns names: FALSE
mode computes statistical mode: FALSE
Factor codes are original numeric labels: FALSE
Single-column extraction always keeps a data frame: FALSE

The earlier worked lessons show the relevant operations directly. For each false statement, name the safer alternative: explicit key matching, frequency tables, label-aware conversion, or drop=FALSE. Knowing the distinction matters more than memorising one function name.