Homework 7 - Strings

Due: Mar 13 by 11:59pm

Weight: This assignment is worth 4% of your final grade.

Purpose: The purposes of this assignment are:

  • To practice manipulating strings in R with the stringr package.
  • To practice computational problem solving with strings.

Assessment: Each question indicates the % of the assignment grade, summing to 100%. The credit for each question will be assigned as follows:

  • 0% for not attempting a response.
  • 50% for attempting the question but with major errors.
  • 75% for attempting the question but with minor errors.
  • 100% for correctly answering the question.

The reflection portion is always worth 10% and graded for completion.

Rules:

  • Problems marked SOLO may not be worked on with other classmates, though you may consult instructors for help.
  • For problems marked COLLABORATIVE, you may work in groups of up to 3 students who are in this course this semester. You may not split up the work – everyone must work on every problem. And you may not simply copy any code but rather truly work together and submit your own solutions.

Readings

The readings from the last week will serve as a helpful reference as you complete this assignment. You can review them here:

Strings

Using the autograder

  • You can check your solutions to problems 2 - 7 by logging into the autograder and uploading your hw7.R file.
  • The file must be named hw7.R or it won’t work.
  • Your user name is your netID, and your password is inside the readme.txt file in the Box folder I shared with you.

1) Staying organized [SOLO, 5%]

Download and use this template for your assignment. Inside the “hw7” folder, open and edit the R script called “hw7.R” and fill out your name, GW Net ID, and the names of anyone you worked with on this assignment.

Writing test functions

For each of the following functions, write a test function first, and then write the function. Your test functions will count for half of the available credit for each problem. Think carefully about the test cases to include in your test functions.

Using good style

For this assignment, you must use good style to receive full credit. Follow the best practices described in this style guide.

2) strToLower(s) [SOLO, 10%]

Write a function that does exactly what str_to_lower() does (i.e. returns the same string but with all letters in lower case) without using str_to_lower() or the Base R tolower() function. Hint: check out the str_replace_all() function!

3) getMiddleCharacter(s) [SOLO, 15%]

Write a function that takes a single string, s, and returns the middle character of the string. If the string has an even number of characters, then return the two middle characters. So getMiddleCharacter("one") should return "n", and getMiddleCharacter("feet") should return "ee".

4) rotateStringLeft(s, k) [COLLABORATIVE, 15%]

Write the function rotateStringLeft(s, k) that takes a string s and a non-negative integer k, and returns the string s rotated k places to the left. So, if s = "iknowkungfu" and k = 2, then the result should be "nowkungfuik". If k is larger than the length of s, the function should continue to rotate the string beyond its starting point. So, if s = "iknowkungfu" and k = 11, then the result should be "iknowkungfu", but if k = 12, the result should be "knowkungfui".

5) isDigit(s) [COLLABORATIVE, 15%]

Write the function isDigit(s) that takes a string s and returns TRUE if all characters in the string are numeric integers and FALSE otherwise. So isDigit("123") should return TRUE, isDigit("123N") should return FALSE, and isDigit("") should return FALSE. Hint: the value '\\d' can be used to search for whether a string has as digit, so str_detect("r2d2", '\\d') would return TRUE but str_detect("rd", '\\d') would return FALSE.

6) getTheGerunds(sentence) [COLLABORATIVE, 15%]

Write a function that takes a single string, sentence, and returns a vector of all the gerunds in it (i.e. all the words that end in "ing"). So getTheGerunds("I like hiking and swimming") should return c("hiking", "swimming"). If there are no gerunds in sentence, the function should return NULL. Hint: first solve how you might separate a single-string sentence into a vector of words.

7) sameChars(s1, s2) [COLLABORATIVE, 15%]

Write the function sameChars(s1, s2) that takes two strings and returns TRUE if the two strings are composed of the same characters (though perhaps in different orders); that is, if every character that is in the first string is in the second (and vice versa), return TRUE, otherwise return FALSE. Assume that s1 and s2 are both strings. This test is case-sensitive, so "ABC" and "abc" do not contain the same characters. The function returns FALSE if either parameter is not a string, but returns TRUE if both strings are empty.

8) Read and reflect [SOLO, 10%]

When we come back from spring break, we’ll be shifting the focus of the class to working with data.

Read and reflect on the following readings to preview what we will be covering next:

Data Analysis
Data Frames

Afterwards, reflect on what you’ve learned while going through these readings and exercises. Is there anything that jumped out at you? Anything you found particularly interesting or confusing?

In a comment (#) in your .R file, write at least a paragraph about your thoughts, and include at least one question. This can be on what you’ve learned and any questions or points of confusion you have about what we’ve covered thus far. This can be related to this assignment, next week’s readings, things going on in the world that remind you something from class, etc. If there’s anything that jumped out at you, write it down.

Some thoughts you may want to try in your reflection:

  • “I used to think ______, now I think ______ 🤔”
  • Discuss some of the key insights or things you found interesting in the readings or recent class periods.
  • Connect the course content to your own work or projects you’re working on.

Submit

Create a zip file of all the files in your R project folder for this assignment, then submit your zip file on the corresponding assignment submission on Blackboard.

Bonus: hasBalancedParentheses(s) [SOLO, 3%]

Write the function hasBalancedParentheses(s), which takes a string s and returns TRUE if the parentheses in s are balanced and FALSE otherwise (ignoring all non-parentheses in the string). We say that parentheses are “balanced” if each right parenthesis closes (matches) an open (unmatched) left parenthesis, and no left parentheses are left unclosed (unmatched) at the end of the text. So, for example, "( ( ( ) ( ) ) ( ) )" is balanced, but "( ) )" is not balanced, and "( ) ) (" is also not balanced. Hint: keep track of how many right parentheses remain unmatched as you iterate over the string.