String Manipulation with Stringr: Understanding Regular Expressions, Study notes of Advanced Computer Programming

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Regular expressions

● A language for describing pa!erns

● "the start of the string, followed by any single character,

followed by one or more digits"

^.[\d]+

Regular expressions

Regular expressions as a pa!ern argument

str_detect(c("R2-D2", "C-3P0"), pattern = START %R% ANY_CHAR %R% one_or_more(DGT)) [1] TRUE FALSE str_view(c("R2-D2", "C-3P0"), pattern = START %R% ANY_CHAR %R% one_or_more(DGT))

In HTML viewer

Let’s practice!

Regular expression review

Pa!ern Regular Expression rebus

Start of string ^ START

End of string $ END

Any single character . ANY_CHAR

Literal dot, carat or dollar

sign

. ^ $ DOT, CARAT, DOLLAR

Alternation

or("dog", "cat") (?:dog|cat) str_view(c("kittycat", "doggone"), pattern = or("dog", "cat"))

(dog|cat)

Repetition

str_view(c("apple", "Aaron"), pattern = one_or_more("Aa"))

Pa!ern Regular Expression rebus

Optional ? optional()

Zero or more * zero_or_more()

One or more + one_or_more()

Between n and m times {n}{m} repeated()

Let’s practice!

Ranges in character classes

DOLLAR %R% char_class("0123456789") $[0123456789] char_class("0-9") [0-9] char_class("a-z") [a-z] char_class("A-Z") [A-Z]

A digit

A lower case le!er

An upper case le!er

Shortcuts

> DGT

\d

WRD \w SPC \s

A digit

A word character

char_class("0-9")

[0-9]

char_class("a-zA-z0-9_") [a-zA-z0-9_]

A whitespace character

Let’s practice!