Measure Twice

stringr First Commit

The first “commit” (code contribution) to the stringr package.

Problem to Solve

The str_length function in the stringr package measures the length of strings. For example, str_length("abc") returns 3, the number of characters in the string.

Of course, the str_length function was written by a programmer like you! Someone, at some point, sat down to create a function that easily measures the length of strings. To be sure the function would work correctly for you, too, they wrote some unit tests to methodically check their work.

In this problem, you’ll build on the work of str_length’s author by writing tests that ensure the function behaves as expected. In a file called test-str_length.R, in a folder called measure, write a set of test cases to thoroughly test the str_length function.

Getting Started

For this problem, you’ll need to create test-str_length.R in a folder called measure.

Create test-str_length.R

Open RStudio per the linked steps and navigate to the R console:

>

Next execute

getwd()

to print your working directory. Ensure your current working directory is where you’d like to create this problem’s folder. If using RStudio through cs50.dev the recommended directory is /workspaces/NUMBER where NUMBER is a number unique to your codespace.

If you do not see the right working directory, use setwd to change it! Try typing setwd("..") if in the working directory of another problem, which will move you one directory higher.

Next execute

dir.create("measure")

in order to create a folder called measure in your codespace.

Now type

setwd("measure")

followed by Enter to move yourself into (i.e., open) that directory. Your working directory should now end with

measure/

Finally, type

file.create("test-str_length.R")

to create a file called test-str_length.R inside of the measure folder.

If all was successful, you should execute

list.files()

and see test-str_length.R. If not, retrace your steps and see if you can determine where you went wrong!

Specification

In test-str_length.R, write a series of testthat tests to thoroughly test the str_length function. As inspiration, consider taking a look at the (actual!) tests for str_length at github.com/tidyverse/stringr/blob/main/tests/testthat/test-length.R. Odds are you should be able to understand most of these tests as written!

You’ll want to begin test-str_length.R by loading both the stringr package and testthat:

library(stringr)
library(testthat)

Below, write at least four tests with at least one test case each. That is, be sure to invoke test_that and an expect function at least four times. Your tests should expect the behavior outlined in the documentation for str_length, stringr.tidyverse.org/reference/str_length.html.

Advice

Unsure what to test? Consider any of the below:

  • Does str_length return the expected output for non-alphabetical characters, such as whitespace, punctuation, or emoji?
  • Does str_length return the expected output for special values such as NA, NaN, Inf, and -Inf?
  • Does str_length return the expected output for vector inputs? What about a data frame as input?

Usage

Assuming test-str_length.R is in your working directory, enter the below in the R console to run your program:

source("test-str_length.R")

How to Test

check50

You can check your code using check50, a program that CS50 will use to test your code when you submit. But be sure to test it yourself as well!

Run the following command in the RStudio console:

check50("cs50/problems/2024/r/measure")

Green smilies mean your program has passed a test! Red frownies will indicate your program output something unexpected. Visit the URL that check50 outputs to see the input check50 handed to your program, what output it expected, and what output your program actually gave.

How to Submit

You can submit your code using submit50.

Keeping in mind the course’s policy on academic honesty, run the following command in the RStudio console:

submit50("cs50/problems/2024/r/measure")