Homework 3: Testing and Tables

Due: Tuesday, February 11th at 11:59 PM

Setup

• Create a file in Pyret called hw3-code.arr. You will write your solution in here. You will need to copy and paste the following at the top of the file. Before starting, change the Pyret context to dcic2024, as described in the CS111 Tables documentation, so that the top of your Pyret file looks like this:

FACULTY-DIR = table: name :: String, department :: String, office :: String, phone :: String
  row: "Strong", "East Asian Studies", "Kassar 180", "282-280-2481"
  row: "Pugh", "Econ", "Gerard 21", "581-280-2510"
  row: "Humphrey", "Physics", "Metcalf 300", "231-121-1129"
  row: "Coleman", "Physics", "B&H 387", "974-093-5128"
  row: "Kaufman", "Music", " ", "502-120-5781"
  row: "Pratt", "Anthro", "CIT 672", "281-6723-5677"
  row: "Cherry", "CS", "CIT 007", "459-005-2098"
  row: "Sosa", "History", "", "878-784-5612"
  row: "Price", "Music", "Kassar 4", "102-503-6002"
  row: "Hopkins", "English", "      ", "742-024-8762"
  row: "Everett", "Physics", "Metcalf 039", "975-202-3333"
  row: "Keller", "French", "Watson 91", "871-458-0235"
  row: "Day", "French", "   ", "441-459-8722"
  row: "Stark", "Anthro", "Maxcy 19", "240-120-7852"
  row: "Branch", "CS", "Robinson 230", "583-0971-2011"
  row: "Brandt", "Bio", "Watson 210", "401-412-9065"
  row: "Moody", "Sociology", "Gerard 721", "206-425-3109"
  row: "Chung", "APMA", "Metcalf 001", "102-030-4050"
end

• Do not put your name anywhere in the file.

Resources

We recommend briefly browsing relevant pages (particularly the CS111 Table documentation, Pyret's String documentation, and the lambda expression documentation) before working on these problems.

• Pyret documentation
• Lambda expressions for tables
• CS111 Table documentation (use this instead of the official Table documentation)
• Strings documentation
• Edstem
• Testing, Design, and Style guide
• Style tip: ALL lines (including comments) must be under 100 characters long

The Assignment

Your friend Coco Cowley (who is a cow) is a student at Cown University, and you are helping her navigate through all of the different departments and professors. In order to find the professors you are looking for, you have to create a way to easily look through the large staff at the university.

Learning Objectives

Our goal this week is to practice several essential skills, including breaking down problems into smaller tasks, using documentation, developing comprehensive collections of tests, and writing functions that takes Row as input. We are also going to think about the tables of data that consumer products collect about people. We're building up to writing programs that process tables as part of doing data analysis (on homework 4 and the first project).

Part 1: Practice Writing Comprehensive Tests

Learning Goal:

• To practice developing a comprehensive set of tests for a function that you didn't write

Knowing how to check whether a program does what you need it to is a valuable skill, even if you aren't the one writing the program. For example, you might have to determine whether a program written (or sold!) by someone else matches your needs. Running a set of specific tests against the existing program can help with this task.

For this problem, imagine that you want to hire a programmer to write a function called is-phone-num that checks if a given string is a valid phone number. A valid phone number is of the format XXX-XXX-XXXX, where each X is a numerical digit.

Your job is to write a check block for is-phone-num. It will look like the following (though you don't need to include our tests):

check "Basic tests for is-phone-num":
  is-phone-num("123-456-7890") is true
  is-phone-num("1") is false
end

You are NOT writing the is-phone-num function itself. The CS111 staff have already done that. In fact, we've written several versions, some that return the answers that you want and some that don't (think of these as proposed solutions from multiple programmers). We are going to grade your check block by running it against all of our versions and seeing whether your tests are comprehensive enough to tell the ones that work from the ones that don't.

How do tests tell apart working and non-working solutions?

Imagine that someone claims to have written a program double that doubles a number. You write a test

check:
  double(2) is 4
end

This will return true on both of the following functions:

fun double(x :: Number) -> x * 2 end  # a correct version
fun double(x :: Number) -> x + 2 end  # an incorrect version

Thus, a check block with only this one test isn't very good, because it doesn't have enough tests to flag that the second version doesn't work. If instead, you wrote the following tests:

check:
  double(2) is 4
  double(3) is 6
end

Now the first function passes both tests while the second function fails one of the tests. This is a more comprehensive test suite because has enough cases to catch errors in the functions. Your job on this assignment will be to figure out a set of tests that catch errors in as many of our broken solutions as you can.

To run your tests against our many versions, you'll work in a custom version of Pyret.

Task 1: Click this link to access the custom Pyret version. It might take some time to load (sometimes even 1-2 minutes), especially the first time. DO NOT click "Begin Implementation".

Pyret/Examplar not loading?

Try removing permissions for Pyret@Brown from your Google account. You can do this by going to Manage your Google Account, searching "apps" in the search bar on top of the page, and removing permissions for Pyret@Brown. Then, revisit the link, log in, and re-allow permissions. If you have any questions, post in Ed or come to hours!

Did you accidentally click "begin implementation?"

Go to drive.google.com, logged in with the account you use for Pyret. Find the folder that is called "pyret.cs.brown.edu" (not code.pyret.org), and delete the file called "is-phone-code.arr". Refresh the examplar page and you should be good to go! Do not delete hw3-tests-examples.arr, since that contains your work!!!

Task 2: Fill in the check block that you see in the custom Pyret window. Your block should contain multiple tests for is-phone-num. As you add tests and hit "Run", the report in the interactions window will show you how many unsatisfactory software products you've ruled out. Pyret is running your tests against seven versions of is-phone-num, only one of which is correct (each of the other six is broken in some way). Your goal is to knock out as many of the six broken ones as you can.

Note: You don't have to knock out all of the unsatisfactory products to do well on this. This is our first exercise that focuses on designing good tests. This week, we're trying to build up your experience writing tests. Aim to knock out at least four, and see if you can get all the way to knocking out all six. You will get full credit for catching four.

Hints on how to approach this

The key to doing well on this is to think systematically about the conditions of the problem and the possible variations in the strings. It will help to have some examples of correctly formatted phone numbers, but also make sure you have plenty of examples with incorrectly formatted phone numbers that should result in false. What might an incorrectly formatted phone number be? Think about the assumptions of the format – for example, the length of the input string, the kind of character that exists at every spot in the string, etc.

Task 3: In your tests file, include a multi-line comment summarizing your strategy and what you learned about writing tests from doing this exercise.

Task 4: Download your tests file (you'll upload it with the code file when you are done with the assignment).

If your tests download as a .zip file, unzip it to retrieve the Pyret file. Make sure your file is called hw3-tests-examples.arr. This will be submitted along with hw3-code.arr to Gradescope. If you also see a downloaded file called hw3-code-ignore.arr, disregard that file.

Task 5: As we begin to work with tabulated data this week, in the form of a faculty directory at Yellow University, we want to ask ourselves where this data comes from. Our goal in tasks 5 and 6 is to think about how we retrieve data and recognize some of the biases in data pre-processing.

Read the following article by Robert Santos from the Urban Institute titled ‘Nonresponse Bias’ Could Explain the Census Bureau’s Finding on the Citizenship Question.

In a separate document titled hw3-src.pdf, respond to the following prompts:

1. In 1-2 sentences, answer the questions: Were you familiar with the United States Census Bureau prior to this assignment? What surprised you about this article? (skim this resource on how the data is collected for more information).
2. In 2-3 sentences, explain what non-response bias is. (skim this page from ScienceDirect for more information).

Task 6: Now read this excerpt from Brookings on how census sampling could be dangerous (if you're interested, here's the full article):

While the 1990 Census reported that 12.05% of adults are African-Americans, the true figure is more like 12.41%. To address undercounting, the Census Bureau has an adjustment mechanism called the Accuracy and Coverage Evaluation. The idea is quite simple—after the first census, the bureau randomly selects particular locations (technically, 11,800 block clusters with 314,000 housing units) and then intensively revisits them. Using this second survey, the Census estimates the number of people who were missed by the first census in various population subgroups (e.g., white males between 19 and 24 living in rural areas). Then the Census uses these undercount estimates to adjust its population estimates. Thus, if 5% of the African-American population is estimated to be missed, the population count for this group will be raised appropriately.

Critics of these techniques argue that they introduce their own errors. This is true, but in ideal circumstances, this procedure will surely improve things. Unfortunately, statistical adjustment also gives much greater discretion to the Census Bureau. The correction procedure is based on population subgroups, and choosing them is very subjective. Do we treat all young urban black males as a subgroup or do we separate them by region? How many ethnic groups do we want to treat as distinct?

This leads to a general point: As you allow for more statistical sophistication, you put more discretion in the hands of the statistician.

In 4-5 sentences, answer the following questions: Do you agree with correcting datasets with mechanisms such as the Census Bureau’s Accuracy and Coverage Evaluation to limit inaccurate figures of underrepresented groups? Are data collectors responsible for disclosing the limitations of the data? (There are no right or wrong answers here, just try to address all of these questions!)

Please submit answers to Tasks 5 & 6 in the separate document called hw3-src.pdf.

Part 2: String validation

Learning Goals:

• To practice writing functions using string functions and boolean operators
• To practice using documentation to find useful built-in functions

Task 7: Write a function in-CIT that takes a String (an office, such as "CIT 429" or "Metcalf 322") and returns a Boolean that indicates whether the office is in the CIT, that is, whether it starts with the characters "CIT " (not including the quotations, and including the space after the T).

Hints:

• Many of the tasks in this section are about which characters are in specific positions in a string. Think about that approach to these problems, and look in the documentation for a String function that helps with this.
• Remember that the first position is a String is numbered 0, not 1.

Note: Being able to look in language documentation for useful operations is an important skill, which is why we aren't telling you exactly which String operations to use. That said, limit yourself to operations with input and output types that we have used this semester (Number, String, Boolean). Don't use operations that return List, as we haven't covered that yet.*

How to Search for Functions in Documentation

When trying to use documentation, read over the names and types of the available functions: do any sound relevant? For those that do, look at the text description and the examples for more detail. If you aren't sure whether a function will help, try a small example on your own in the interactions window.

Task 8: Write a function called in-building that takes a String (an office) and another String (a building) and returns a Boolean that indicates whether the office is in that building, that is, whether it starts with the building name followed by a space.

Task 9: Write a function called get-room-number that takes in a String (an office) and returns a String of only the office number. For example, get-room-number("CIT 429") should return "429" (as a String). The room number of an office is the part of the String that follows the first space. If the input string does not have a space, it should raise("Malformed input: no spaces"). We've seen an example of raise in the get-grade function in the Feb 5 lecture (take a look at the starter code). Here is the Pyret documentation.

How do we test if a function raises?

You can use raises instead of is! See the Pyret documentation

Part 3: Lookup operations

We will cover the material for part 3 on Feb 7.

Learning Goals:

• To give you practice accessing data from tables
• To help you understand the benefit of bundling small pieces of data into one larger piece of data

Take a look at the FACULTY-DIR table in your Pyret file (you can see it in full by typing FACULTY-DIR in the interactions window), which represents a directory of university faculty. Notice it has the columns "name", "department", "office", and "phone".

Part 3A: Using helper functions on Rows

Remember that we have an explainer on using lambda expressions and Tables. Be careful of boolean redundancy!

Copy-paste the following code, which pulls out some Rows from FACULTY-DIR.

strong-row = FACULTY-DIR.row-n(0)
pratt-row = FACULTY-DIR.row-n(5)

The following tasks are warmups to writing lambda expressions. They're meant to get you to practice writing expressions on specific rows (strong-row) and (pratt-row) before we move on to the generalized tasks in the next part. You are not writing functions or lambda expressions for tasks 10 and 11. Don't overthink these tasks – the expressions will be very simple.

Task 10: Write a single-line expression that uses in-CIT to check if strong-row has an office that is in the CIT. This expression will evaluate to false. Now, repeat this for pratt-row, which should evaluate to true (the only difference between the two expressions should be that strong-row gets replaced with pratt-row).

Task 11: Write a single-line expression that uses get-room-number to get the room number of Strong's office from strong-row. Run your code and make sure that the output in the right side of the Pyret window has the correct room number.

Part 3B: Table operations with helper functions

Note: It is extremely important that you use the CS0111 Table documentation, not the Pyret Table documentation. The 111 version includes the documentation for Rows, which is necessary for this assignment.

Task 12: Write an expression for computing the table of all of the directory entries of faculty in FACULTY-DIR who have offices in the CIT. The result of this expression should be stored with the name rows-in-CIT (e.g. you should have something of the form rows-in-CIT = [some expression to compute the table] in your code).

Hints on the lambda expression

You will use a lambda expression for this task that generalizes your computation from Task 10. Remember that task 10 had you write expressions for specific rows of FACULTY-DIR, and now you're writing an expression that generalizes to any row in FACULTY-DIR. You should be able to make a lambda expression by replacing strong-row/pratt-row from your expressions in Task 10 with r and surrounding the computation with lam(r): and end. Said otherwise, you're defining an anonymous/nameless function (the lambda) that takes in as input an arbitrary row r from FACULTY-DIR.

Task 13: Some faculty in the directory do not have offices listed. In those cases, the "office" cell of that row is a String of 0 or more spaces (e.g. "" or " "). Write an expression for computing a table of all of the directory entries in FACULTY-DIR who do not have an office listed. Your expression should make use of a helper function (one option is for this helper to take in a String and return a String, but you might have a different approach). Remember to write tests for this helper function. The resulting table should be stored with the name no-office-fac.

Hint:

The helper function should be used to help determine if a String is only made up of spaces. There are at least two ways to do this using functions in the Pyret String documentation – by transforming the original String, or by generating a new String to compare against.

Task 14: Write a computation to determine the name of the faculty member who has the largest listed office number on campus (as determined alphabetically, e.g. using String sorting). You might have to use multiple lines to compute intermediate data, but the name should be stored with the name largest-office-fac. Just like in the hint for task 12, refer back to Task 11 for help with the lambda expression. If the result surprises you, that's the point – keep reading the handout 🐮

Hint:

Faculty who don't have an office listed by definition cannot have the largest office number. How can you make sure that the error raised by get-room-number does not cause an error in this computation?

What office number does that faculty member have? Examine FACULTY-DIR by looking through it manually – does the result surprise you? Are there larger office numbers in the table?

Task 15: In a comment right below the expression for Task 14, write 1-2 sentences on why the office number for the faculty member that you determined in Task 14 may not be the numerically largest office number in the directory. Your answer should demonstrate knowledge of data types.

Task 16: Write a set of expressions to determine whether all the offices for the Physics faculty (faculty with the department "Physics") are located on the 3rd floor. An office on the third floor has a number with three digits, where the first digit is 3 (for example, "CIT 368" is on the third floor, while "Metcalf 30" is not). Assume all Physics faculty have an office listed in the table. The result of the computation should be a Boolean stored with the name all-physics-third-floor.

Hint:

There are multiple ways how to approach this task. Write down a to-do list of the intermediate computation(s) you might need. Where does it make sense to apply a table operation? Where does it make sense to make a helper function?

Task 17: Write a function called get-phone that takes in a faculty name (as a String) and returns that faculty member's phone number as a String. If a faculty member of that name is not in FACULTY-DIR, this function should raise("faculty name not in table"). You can assume that names are unique in this table, that is, no two faculty have the same name.

Check Block (Autograder Compatibility)

When you complete all the tasks of this homework, please copy the following check block into the bottom of your code file!

The check block will be checking that all required functions and names are included, correctly named, and that they handle inputs in the right order. This is the bare minimum for the autograder to function properly – do not edit this!

check "functions exist and have correct inputs": 
  in-CIT("") is false
  in-building("", "") is false
  is-string(get-room-number("CIT 333")) is true
  is-table(rows-in-CIT) is true
  is-table(no-office-fac) is true
  is-string(largest-office-fac) is true
  is-boolean(all-physics-third-floor) is true
  is-string(get-phone("Strong")) is true
end 

If you see this block appear in the interactions window after running it, then you are fine! Please submit to Gradescope.

If not, double-check your function names, input types, and input order. If you are still stuck, please feel free to come to hours or post on Ed!

Handin

• Download both your solutions file and your test file (instructions about creating the test file are in Part 2) and make sure they are called hw3-code.arr and hw3-tests-examples.arr respectively. Download your written responses as hw3-src.pdf. Hand in your work on Gradescope in the assignment named "Homework 3," and remember to include all three files in your submission!

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drive ME crazy! by Lil Yachty

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Brown University CSCI 0111 (Spring 2025)
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