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Intermediate Regular Expressions in R

Angelo Zehr

Data Journalist

Where you might have left off

String Manipulation with stringr in R

From Rebus to writing custom expressions

Does "cat" start with "c"?

The rebus way:

str_detect("cat", pattern = START %R% "c")

Regular expression:

str_detect("cat", pattern = "^c")

Prerequisites: stringr

str_detect(string, pattern)

str_match(string, pattern)

What regular expressions will help you achieve

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What regular expressions will help you achieve

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Our first dataset

movie_titles <- c(
  "Karate Kid",
  "The Twilight Saga: Eclispe",
  "Knight & Day",
  "Shrek Forever After (3D)",
  "Marmaduke.",
  "Predators",
  "StreetDance (3D)",
  "Robin Hood",
  "Micmacs A Tire-Larigot",
  "Sex And the City 2",
...

movie_titles[
  str_detect(
    movie_titles,
    pattern = "^K"
  )
]

"Karate Kid",
"Knight & Day",
...

Special characters in regular expressions

Special character	Meaning
`^`	Caret: Marks the beginning of a line or string
`$`	Dollar Sign: Marks the end of a line or string
`.`	Period: Matches anything: letters, numbers or white spaces
`\\.`	Two backslashes: Escapes the period when we search an actual period

For example

Code	Result
`str_match("Book", "^.")`	Will match `"B"`
`str_match("Book", ".$")`	Will match `"k"`
`str_match("Book", "\\.")`	No match
`str_match("Book.", "\\.")`	Will match `"."`

Let's practice!

Intermediate Regular Expressions in R