Homework 3

Moiya Josephs 2/17/2022

library(stringr)

Question 1

Using the 173 majors listed in fivethirtyeight.com’s College Majors dataset [https://fivethirtyeight.com/features/the-economic-guide-to-picking-a-college-major/], provide code that identifies the majors that contain either “DATA” or “STATISTICS”

college_major <- read.csv("https://raw.githubusercontent.com/fivethirtyeight/data/master/college-majors/majors-list.csv", header = TRUE)

college_major$Major %>% str_subset("DATA|STATISTICS")

## [1] "MANAGEMENT INFORMATION SYSTEMS AND STATISTICS"
## [2] "COMPUTER PROGRAMMING AND DATA PROCESSING"     
## [3] "STATISTICS AND DECISION SCIENCE"

Question 2

Write code that transforms the data below:

character <- '[1] "bell pepper"  "bilberry"     "blackberry"   "blood orange"
[5] "blueberry"    "cantaloupe"   "chili pepper" "cloudberry"  
[9] "elderberry"   "lime"         "lychee"       "mulberry"    
[13] "olive"        "salal berry"'

#c2<- str_replace_all(character2, regex("\\s{2,}|\\[[1-9]\\]"), " ")
# c2<- str_replace_all(character, regex("\\[[1-9]\\]"), " ")
# c2<- str_replace_all(c2, regex("\\s{2,}"), ",")
# c2<- str_replace_all(c2,fixed(""),"")

c2<- unlist(str_extract_all(character,'[[A-Za-z]]+\\s[[A-Za-z]]+|[[A-Za-z]]+'))
c3<- dput(as.character(c2))

## c("bell pepper", "bilberry", "blackberry", "blood orange", "blueberry", 
## "cantaloupe", "chili pepper", "cloudberry", "elderberry", "lime", 
## "lychee", "mulberry", "olive", "salal berry")

Question 3

Describe, in words, what these expressions will match:

For R an additional backslash needs to be added.

• “(.)\1\1”
• “(.)(.)\2\1”
• “(..)\1” - “(.).\1.\1”
• “(.)(.)(.).*\3\2\1”

A

This regex will match any character because of the . in the capturing group (except for line terminators) at least three times. Once because of the capturing group. The second and third string is because \1 repeated twice.

p1<- "www"
str_detect(p1,"(.)\\1\\1")

## [1] TRUE

B

Both (.) will match any two characters each belonging to seperate capturing groups. The 2 and 1 means the same two characters must be repeated the 2 first, then the one.

Some examples include:

# original regex - "(.)(.)\\2\\1"  Added extra \ because of escaping
p2<- "weew"

str_detect(p2,"(.)(.)\\2\\1")

## [1] TRUE

C

Since there are two periods in the capturing group this regex will match with any two characters that repeat at least once. (Since there is no termination specified). Some examples
wwww
wwwwww

p3<- "wwww"
str_detect(p3,"(..)\\1")

## [1] TRUE

D

“(.).\1.\1”

(.) means any character in a capturing group. The . means there’s an additional character. The double backslash 1 means the original character should be repeated. The extra . means another character and the 1 refers to the original character.

An example:

p4<- "apa.a"
str_detect(p4,"(.).\\1.\\1")

## [1] TRUE

E

“(.)(.)(.).*\3\2\1”
This regex expression indicated the string must have three of any character, with any other characters afterwards as long as it ends with the original 3 backwards.

An example:

p4<- "abccba"
str_detect(p4,"(.)(.)(.).*\\3\\2\\1")

## [1] TRUE

Question 4

Construct regular expressions to match words that:

A. Start and end with the same character.

four_a <- "abbbba"
str_detect(four_a,"^(.).*\\1$")

## [1] TRUE

B. Contain a repeated pair of letters (e.g. “church” contains “ch” repeated twice.)

four_b <- "church"
str_detect(four_b,"(..).*\\1")

## [1] TRUE

C. Contain one letter repeated in at least three places (e.g. “eleven” contains three “e”s.)

four_c <- "eleven"
str_detect(four_c,"(.).*\\1.*\\1")

## [1] TRUE