Regex in R

This lesson is called Regex in R, part of the Data Cleaning with R course. This lesson is called Regex in R, part of the Data Cleaning with R course.

Transcript

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Your Turn

Solution

##%######################################################%##
#                                                          #
####               Regex in R - Your Turn               ####
#                                                          #
##%######################################################%##


# Match the following regular expressions against the test vector below using `str_detect`.  
## Can you explain the matches?

# Regular expressions

# 1. ^dog
# 2. ^[a-z]+$
# 3. \\d

test_vector <- c("Those dogs are small.","dogs and cats",
                 "34","(34)","rat","watchdog","placemat",
                 "BABY","2011_April","mice")


# load packages -----------------------------------------------------------
library(stringr)

# create text string ------------------------------------------------------
test_vector <- c("Those dogs are small.","dogs and cats",
                 "34","(34)","rat","watchdog","placemat",
                 "BABY","2011_April","mice")

# evaluate if each element contains a match -------------------------------
# match the literal string dog
str_detect(test_vector,"^dog") # second element contains match

# match lowercase
str_detect(test_vector,"^[a-z]+$") # elements 5,6,7, and 10 matched 

# match numbers
str_detect(test_vector,"\\d") # elements 3,4, and 9 matched

Match the following regular expressions against the test vector below using str_detect. Can you explain the matches?

Regular expressions

^dog
^[a-z]+$
\\d

test_vector <- c("Those dogs are small.","dogs and cats",
                 "34","(34)","rat","watchdog","placemat",
                 "BABY","2011_April","mice")

Learn More

To learn more about the stringr package, check out the documentation website. There is also a stringr cheatsheet. You also might check out Chapter 14 of R for Data Science as well as this blog post by Hugo Toscano on working with strings in R.

Have any questions? Put them below and we will help you out!

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Alberto Cabrera • January 6, 2024

Need your help figuring out how the following regex works : "\[.+\]|\?". It was developed by Albert Rapp as part of a mutate program to pull years form the following strings. "1973 [YR1973]" "1974 [YR1974]" "1975 [YR1975]" "1976 [YR1976]"

wd_data %>% mutate( year = year %>% str_remove("\[.+\]|\?") %>% str_to_title()) %>% pull(year)

It is not clear to me how this regular expression worked in extracting just the first 4 characters associated with year. Thanks