Regex Syntax¶
- R Regular Expression Cheat Sheet Grade
- R Regular Expression Cheat Sheet Answer
- Regular Expression Cheat Sheet R
Characters¶| Character | Matches |
|---|
a | a character |
. | Any character (except newline) |
. | . character |
| |
* | * character |
R Markdown Cheatsheet R Markdown is an authoring format that makes it easy to write reusable reports with R. You combine your R code with narration written in markdown (an easy-to-write plain text format) and then export the results as an html, pdf, or Word file. You can even use R Markdown to build interactive documents and slideshows. Gregexpr looks for the given regular expression in string; perl = TRUE allows for the 'look ahead' and 'look behind' functionality; regmatches pulls out the matching piece of the string using the regular expression.
Character Classes¶| Matches | Description |
|---|
[abcd] | Any one of the letters a through d | Set of characters |
[^abcd] | Any character but a, b, c, or d | Complement of a set of characters |
[a-d] | Any one of the letters a through d | Range of characters |
[a-dz] | Any of a, b, c, d, or z | Range of characters |
Special Sequences¶| Type | Expression | Equivalent To | Description |
|---|
| Word Character | w | [a-zA-Z0-9_] | Alphanumeric or underscore |
|---|
| Non-word Character | W | [^a-zA-Z0-9_] | Anything but a word character |
|---|
| Digit Character | d | [0-9] | Numeric |
|---|
| Non-digit Character | D | [^0-9] | Non-numeric |
|---|
| Whitespace Character | s | [tnrfv] | Whitespace |
|---|
| Non-whitespace Character | S | [^tnrfv] | Anything but a whitespace character |
|---|
Anchors¶| Anchor | Matches |
|---|
^ | Start of the string |
$ | End of the string |
b | Boundary between word and non-word characters |
Groups¶| Group Type | Expression |
|---|
| Capturing | ( ... ) |
| Non-capturing | (?: ... ) |
Quantifiers/Repetition¶| Quantifier | Modification |
|---|
{5} | Match expression exactly 5 times |
{2,5} | Match expression 2 to 5 times |
{2,} | Match expression 2 or more times |
{,5} | Match expression 0 to 5 times |
* | Match expression 0 or more times |
{,} | Match expression 0 or more times |
? | Match expression 0 or 1 times |
{0,1} | Match expression 0 or 1 times |
+ | Match expression 1 or more times |
{1,} | Match expression 1 or more times |
Non-greedy quantifiers¶| Quantifier | Modification |
|---|
{2,5}? | Match 2 to 5 times (less preferred) |
{2,}? | Match 2 or more times (less preferred) |
{,5}? | Match 0 to 5 times (less preferred) |
*? | Match 0 or more times (less preferred) |
{,}? | Match 0 or more times (less preferred) |
?? | Match 0 or 1 times (less preferred) |
{0,1}? | Match 0 or 1 times (less preferred) |
+? | Match 1 or more times (less preferred) |
{1,}? | Match 1 or more times (less preferred) |
Alternators¶| Quantifier | Modification |
|---|
ABC|DEF | Match string ABC or string DEF |
Lookaround¶| Quantifier | Modification |
|---|
(?=abc) | Zero-width match confirming abc will match upcoming chars |
(?!abc) | Zero-width match confirming abc will not match upcoming chars |
Python¶
functions¶| Function | Purpose | Usage |
|---|
re.search | Return a match object if pattern found in string | re.search(r'[pat]tern','string') |
re.finditer | Return an iterable of match objects (one for each match) | re.finditer(r'[pat]tern','string') |
re.findall | Return a list of all matched strings (different when capture groups) | re.findall(r'[pat]tern','string') |
re.split | Split string by regex delimeter & return string list | re.split(r'[-]','st-ring') |
re.compile | Compile a regular expression pattern for later use | re.compile(r'[pat]tern') |
flags¶| Flag | Description |
|---|
re.IGNORECASE | Match uppercase and lowercase characters interchangeably |
re.VERBOSE | Ignore whitespace characters and allow # comments |
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R Regular Expression Cheat Sheet Grade
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R Regular Expression Cheat Sheet Answer
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