Replacing Text

Part of the Logic & Flow section of Coddy's R journey. Lesson 5 of 64.

sub(pattern, replacement, x) replaces the first match in each string, and gsub() replaces every match. As with grepl(), fixed = TRUE treats the pattern as plain text.

date <- "2024-01-15"
print(sub("-", "/", date, fixed = TRUE))
print(gsub("-", "/", date, fixed = TRUE))

Output:

[1] "2024/01-15"
[1] "2024/01/15"

Replacing with an empty string deletes the matches. This cleans text before converting it to a number:

price <- "$1,299.00"
clean <- gsub(",", "", sub("$", "", price, fixed = TRUE), fixed = TRUE)
print(clean)
print(as.numeric(clean) * 2)

Output:

[1] "1299.00"
[1] 2598

Without fixed = TRUE the pattern is a regular expression. Two useful pieces: [0-9] matches any digit, and + repeats the piece before it one or more times, so " +" matches a run of spaces.

msg <- "call  me   at 555 0199"
print(gsub(" +", " ", msg))
print(gsub("[0-9]", "#", msg))

Output:

[1] "call me at 555 0199"
[1] "call  me   at ### ####"

Like the other string functions, sub() and gsub() work on every element of a vector:

codes <- c("a-1", "b-22", "c-3")
print(gsub("-", "", codes, fixed = TRUE))
print(sub("-[0-9]+", "", codes))

Output:

[1] "a1"  "b22" "c3" 
[1] "a" "b" "c"

Challenge

Easy

Complete slugify(title). Return the title in lower case, without spaces at the start or end, and with every run of spaces replaced by a single -: Hello World becomes hello-world.

The supplied code reads the title and prints the returned value.

Try it yourself

slugify <- function(title) {
  # Write your code here
  title
}

# Supplied input/output code: keep it as it is
input <- suppressWarnings(readLines(file("stdin")))
cat(slugify(input[1]), sep = "\n")