![Definition ofTerms
Characters(Metacharacters): d = digits while D represents non digits, w
represents word etc.
Quantifiers: + = one or more, ?= once or more, * = zero or more and { } for
specifying minimum, maximum or both.
Logic: | = or, (...)= Group1 2 3 = Contents of group 1,2,3) you can also use
negate a value in group by using (?: ...) e.g. (?:lunalo|John)= John
Character Classes: Denoted by [...] provides ranges of characters.
Anchors: Declare boundaries e.g. ^ for start and $ for end POSIX Classes:
e.g. [:punct:] for punctuations. and [:alpha:] for alphabets.
Look rounds:(?=...)= Positive look ahead (?<=...)= Positive lookbehind
(?!...)= Negative look ahead (?<!..)= Negative look behind.](https://image.slidesharecdn.com/stataregexp-180610120422/85/Regular-Expressions-in-Stata-4-320.jpg)
![Regular Expressions Symbols in Stata
Quantifiers symbols:
Metacharacters
* match zero or more of the preceding expression
+ Match one or more of the preceding expression
? Match either zero or one of the preceding expression
a–z match a range of characters or numbers .The “a” and “z” are an example. It could also be 1-9, etc.
This is used together with square characters. e.g. [1-9].
. match any character
It used for Escaping a metacharacter](https://image.slidesharecdn.com/stataregexp-180610120422/85/Regular-Expressions-in-Stata-5-320.jpg)
![Regular Expressions Symbols in
Stata
Anchors
Groups
Logic
^ Match expression at beginning of string. E.g. “^[hj]” matches hj at the beginning of the
string. Be careful this “[^hj]” will negate hj in a string.
$ Match expression at end of string. E.g. “hj$” will match hj at the end of the string.
( ) Subexpression e.g. (1-9) (a-z) etc.
| The vertical bar /pipe character signifies a logical “or”](https://image.slidesharecdn.com/stataregexp-180610120422/85/Regular-Expressions-in-Stata-6-320.jpg)
Regular Expressions in Stata
- 1. Regular Expressions for Data Management in STATA John Lunalo
- 2. Overview 1. Introduction 2. Definition of terms 3. Regular Expressions Symbols in STATA 4. Regular Expressions Commands in Stata 5. Examples
- 3. Introduction Regular expressions (regex/regexp/rational expressions) are special characters that defines a search pattern. Types of Regular Expressions Extended Regular Expressions: Used majorly by programming languages. Default in those languages. Perl-Like Regular Expressions: Use syntax and semantics of Perl Language Literal/Fixed Regular Expressions: Most basic although it can still be combined with special characters for complex pattern.
- 4. Definition ofTerms Characters(Metacharacters): d = digits while D represents non digits, w represents word etc. Quantifiers: + = one or more, ?= once or more, * = zero or more and { } for specifying minimum, maximum or both. Logic: | = or, (...)= Group1 2 3 = Contents of group 1,2,3) you can also use negate a value in group by using (?: ...) e.g. (?:lunalo|John)= John Character Classes: Denoted by [...] provides ranges of characters. Anchors: Declare boundaries e.g. ^ for start and $ for end POSIX Classes: e.g. [:punct:] for punctuations. and [:alpha:] for alphabets. Look rounds:(?=...)= Positive look ahead (?<=...)= Positive lookbehind (?!...)= Negative look ahead (?<!..)= Negative look behind.
- 5. Regular Expressions Symbols in Stata Quantifiers symbols: Metacharacters * match zero or more of the preceding expression + Match one or more of the preceding expression ? Match either zero or one of the preceding expression a–z match a range of characters or numbers .The “a” and “z” are an example. It could also be 1-9, etc. This is used together with square characters. e.g. [1-9]. . match any character It used for Escaping a metacharacter
- 6. Regular Expressions Symbols in Stata Anchors Groups Logic ^ Match expression at beginning of string. E.g. “^[hj]” matches hj at the beginning of the string. Be careful this “[^hj]” will negate hj in a string. $ Match expression at end of string. E.g. “hj$” will match hj at the end of the string. ( ) Subexpression e.g. (1-9) (a-z) etc. | The vertical bar /pipe character signifies a logical “or”
- 7. Regular Expressions Commands in StataIn Stata we have three commands that uses regular expressions in their operations:- 1) regexm 2) regexr 3) regexs M- Matches. it is Boolean R- Replace S- Subexpression
- 8. Examples Example Datasets to be used to experiment on three commands
Editor's Notes
- #5: Characters with special meaning Represents the number of times you want a character, literal or a pattern as a whole needs to appear in a regular expressions Defining arrangement of patterns.