UBC STAT545 2015 cm103: Introduction to Regular Expressions

One part of a STAT545 lecture from 2015.

Transcript

1. Regular Expressions & Character Data in R Kieran Samuk for STAT545
2. Outline 1. Regular expression basics 2. Regular expressions & character data in R
3. Outline 1. Regular expression basics 2. Regular expressions & character data in R
4. Regular expressions (“regex”) Coded representations of patterns in text
5. Regex is (mostly) universal Not limited to a specific programming language
6. Insanely useful for… Filtering Finding and replacing Validating input Counting occurrences Mining text
7. Regex Anatomy ^[Hh]e walked [0-9]* meters$
8. Regex Anatomy ^[Hh]e walked [0-9]* meters$ “Literals” “Metacharacters” Normal letters and digits (+ spaces) Special characters with regex specific functions
9. Regex Anatomy ^[Hh]e walked [0-9]* meters$ “Literals” “Metacharacters” Normal letters and digits (+ spaces) Special characters with regex specific functions
10. Go to https://regex101.com/r/gZ2uW4/2
11. Literals All literals match themselves, and only themselves
12. Metacharacters: Groups and Ranges . Any character [AaBb] A or a or B or b [A-Z] A or B or C, … Z [0-9] 0 or1 or 2, … 9 [^A-Z] Everything but capitals (it|the) “it” OR “the”
13. Metacharacters: Quantifiers * Zero or more times + One or more times ? Zero or one times {3} Exactly 3 times {1,3} 1 to 3 times {3,} 3 or more times
14. Metacharacters: Other ^ Start of a string $ End of a string \ Escape (meta to literal) \w, \W [A-Za-z0-9], [^A-Za-z0-9] \d, \D [0-9], [^0-9] \s, \S Whitespace (space, tab, newline, carriage return, etc.) + not
15. Metacharacters: Other ^ Start of a string $ End of a string \ Escape (meta to literal) \w, \W [A-Za-z0-9], [^A-Za-z0-9] \d, \D [0-9], [^0-9] \s, \S Whitespace (space, tab, newline, carriage return, etc.) + not
16. Regex Challenges! RULES 1. Match ONLY the target elements 2. Each discrete item must be a separate match 3. THERE ARE CANDY PRIZES 1. DNA sequences 2. Email addresses 3. Smilies 4. HTML Tags (each tag separately) 5. Phone numbers 6. URLs 7. Macho Man Randy Savage Quotations 9. Citations
17. Notes Only a glimpse of regex! Lots of resources on the web
18. Outline 1. Regular expression basics 2. Regular expressions & character data in R
19. Outline 1. Regular expression basics 2. Regular expressions & character data in R