Signal a passing or failing grade if two values are equal

pass_if_equal() and fail_if_equal() are two graded() helper functions that signal a passing or a failing grade if two values are equal. They are designed to easily compare the returned value of the student's submitted code with the value returned by the solution or another known value:

• Both functions find and use .result as the default for x, the first item in the comparison. .result is the last value returned from the user's submitted code.

• pass_if_equal() additionally finds and uses .solution as the default expected value y.

See graded() for more information on gradethis grade-signaling functions.

pass_if_equal(
  y = .solution,
  message = getOption("gradethis.pass", "Correct!"),
  x = .result,
  ...,
  env = parent.frame(),
  praise = getOption("gradethis.pass.praise", FALSE)
)

fail_if_equal(
  y,
  message = getOption("gradethis.fail", "Incorrect"),
  x = .result,
  ...,
  env = parent.frame(),
  hint = getOption("gradethis.fail.hint", FALSE),
  encourage = getOption("gradethis.fail.encourage", FALSE)
)

Arguments

y	The expected value against which x is compared using waldo::compare(x, y). In pass_if_equal(), if no value is provided, the exercise .solution, or the result of evaluating the code in the exercise's *-solution chunk, will be used for the comparison.
message	A character string of the message to be displayed. In all grading helper functions other than graded(), message is a template string that will be processed with glue::glue().
x	First item in the comparison. By default, when used inside grade_this(), x is automatically assigned the value of .result — in other words the result of running the student's submitted code. x is not the first argument since you will often want to compare the final value of the student's submission against a specific value, y.
...	Additional arguments passed to graded()
env	environment to evaluate the glue message. Most users of gradethis will not need to use this argument.
praise	Include a random praising phrase with random_praise()? The default value of praise can be set using gradethis_setup() or the gradethis.pass.praise option.
hint	Include a code feedback hint with the failing message? This argument only applies to fail() and fail_if_equal() and the message is added using the default options of give_code_feedback() and maybe_code_feedback(). The default value of hint can be set using gradethis_setup() or the gradethis.fail.hint option.
encourage	Incude a random encouraging phrase with random_encouragement()? The default value of encourage can be set using gradethis_setup() or the gradethis.fail.encourage option.

Value

Returns a passing or failing grade if x and y are equal.

Functions

• pass_if_equal: Signal a passing grade only if x and y are equal.

• fail_if_equal: Signal a failing grade only if x and y are equal.

See also

Other grading helper functions: graded(), pass(), fail(), pass_if(), fail_if(), pass_if_equal(), fail_if_equal().

Examples

# Suppose our prompt is to find the cars in `mtcars` with 6 cylinders...

grader <- 
# ```{r example-check}
  grade_this({
    # Automatically pass if .result equal to .solution
    pass_if_equal()
    
    fail_if_equal(mtcars[mtcars$cyl == 4, ], message = "Not four cylinders")
    fail_if_equal(mtcars[mtcars$cyl == 8, ], message = "Not eight cylinders")
    
    # Default to failing grade with feedback
    fail()
  })
# ```

.solution <- 
# ```{r example-solution}
  mtcars[mtcars$cyl == 6, ]
# ```

# Correct!
grader(mock_this_exercise(mtcars[mtcars$cyl == 6, ], !!.solution))
#> <gradethis_graded: [Correct] Success! Correct!>

# These fail with specific messages
grader(mock_this_exercise(mtcars[mtcars$cyl == 4, ], !!.solution))
#> <gradethis_graded: [Incorrect] Not four cylinders>
grader(mock_this_exercise(mtcars[mtcars$cyl == 8, ], !!.solution))
#> <gradethis_graded: [Incorrect] Not eight cylinders>

# This fails with default feedback message
grader(mock_this_exercise(mtcars[mtcars$mpg == 8, ], !!.solution))
#> <gradethis_graded: [Incorrect]
#>   Incorrect. I expected you to call `structure()` where you called `[`.
#>   Please try again.
#> >