Due: 26 October by 11:00 pm

Purpose, Skills, & Knowledge: The purposes of this assignment are:

• To practice manipulating strings in R with the stringr library.
• 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.

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.
• Even though you work collaboratively, you still must submit your own solutions.

### 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.

### 2) strToLower(s) [SOLO, 15%]

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 numbers and in different orders); that is, if every character that is in the first string is in the second (and vice versa), and FALSE otherwise. 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) Submit your files [SOLO, 5%]

Create a zip file of all the files in your R project folder for this assignment and submit the zip file on Blackboard (note: to receive full credit, your submission must follow the above format of using a correctly-named R Project and .R script).

### 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.

EMSE 4574: Programming for Analytics (Fall 2020) |
Tuesdays | 12:45 - 3:15 PM | Dr. John Paul Helveston | jph@gwu.edu
Content 2020 John Paul Helveston. See the licensing page for details.