Strings

2020

Libraries

library(stringr)

Length

str_length1 The length of a string function:

str_length("Party Parrot")
#> [1] 12

Combining

Individual strings

str_c2 Join multiple strings into a single string function:

str_c("What's", " ", "next", "?")
#> [1] "What's next?"

sep argument:

str_c("Secret", "plan", "to", "fight", "inflation", sep = " ")
#> [1] "Secret plan to fight inflation"

Vectors

str_c("file", 1:5)
#> [1] "file1" "file2" "file3" "file4" "file5"

collapse argument:

str_c("file", 1:5, collapse = ", ")
#> [1] "file1, file2, file3, file4, file5"

Splitting

str_split3 Split up a string into pieces function:

str_split("Have a cookie Sam", " ")
#> [[1]]
#> [1] "Have"   "a"      "cookie" "Sam"

Extract the results vector using unlist:

unlist(str_split("Have a cookie Sam", " "))
#> [1] "Have"   "a"      "cookie" "Sam"

Subsetting

str_sub4 Extract and replace substrings from a character vector function:

str_sub("They're all about duty", 1, 4)
#> [1] "They"

Negative indicies index from the end:

str_sub("Washington Dulles International Airport: IAD", -3, -1)
#> [1] "IAD"

Transforming

Case change

str_to_upper, str_to_lower, str_to_title, str_to_sentence5 Convert case of a string. functions:

str_to_lower("LINCOLN MEMORIAL")
#> [1] "lincoln memorial"
str_to_upper("LINCOLN MEMORIAL")
#> [1] "LINCOLN MEMORIAL"
str_to_title("LINCOLN MEMORIAL")
#> [1] "Lincoln Memorial"
str_to_sentence("LINCOLN MEMORIAL")
#> [1] "Lincoln memorial"

Trimming

str_trim and str_squish6 Trim whitespace from a string functions:

s <- "   Big   Bird"
writeLines(s)
#>    Big   Bird
writeLines(str_trim(s))
#> Big   Bird
writeLines(str_squish(s))
#> Big Bird

Regular Expressions

Detecting matches

str_detect7 Detect the presence or absence of a pattern in a string function:

sentences <- c("You're a smart savvy woman who could easily consider world domination for a next career move.",
               "I'm going to crush him. I'm going to make him cry and then I'm going to tell his momma about it.",
               "Never doubt that a small group of thoughtful committed citizens can change the world.")
str_detect(sentences, "world")
#> [1]  TRUE FALSE  TRUE

Extracting matches

str_extract and str_extract_all8 Extract matching patterns from a string functions:

header <- '
---
title: "Two Cathedrals"
author: "Aaron Sorkin"
date: "May 16, 2001"
---
'
str_extract(header, "title:.*")
#> [1] "title: \"Two Cathedrals\""

Replacing

str_replace and str_replace_all9 Replace matched patterns in a string functions:

str_replace(sentences[2], "I'm going to", "I will")
#> [1] "I will crush him. I'm going to make him cry and then I'm going to tell his momma about it."
str_replace_all(sentences[2], "I'm going to", "I will")
#> [1] "I will crush him. I will make him cry and then I will tell his momma about it."
library(magrittr)
str_extract(header, "title:.*") %>%
    str_replace("title:[ ]*", "") %>%
    str_replace_all("\"", "")
#> [1] "Two Cathedrals"

Globs

Convert a glob to a regular expression via glob2rx10 Change Wildcard or Globbing Pattern into Regular Expression function:

dir(pattern = glob2rx("*.Rmd"))
#> "eda.Rmd" "report.Rmd"