Using "grepl" for string detection (R)

grepl function is use to return TRUE if a string contain the pattern that we specify, else it will return FALSE if the parameter is not match in each element of the vector.

general function of grepl:

grepl(pattern, x, ignore.case=F, perl=F, fixed = F, useBytes=F)

• pattern = regular expression, or string for fixed = TRUE.

• x = string, the character vector

• ignore.case = logical, should perl-compatible regexps be used? has priority over extended.

• fixed = logical, if TRUE the pattern is a string to be matched as is. Overrides all conflicting arguments.

• useBytes = logical, if TRUE the matching is done byte-by-byte rather than character-by-character.

x <- "line 4322: He is now 25 years old, and weights 130lbs" > y <- grepl("\\d+",x) > y

[1] TRUE

x <- "line 4322: He is now 25 years old, and weights 130lbs" > y <- grepl("[[:digit:]]",x) > y

[1] TRUE

Vector match:

str <- c("Regular", "expression", "examples of R language") >x <- grepl("x*ress",str) >x

[1] FALSE TRUE FALSE

---

REGULAR EXPRESSION CODING:

Syntax Description

\\d ---> Digit, 0,1,2 ... 9

\\D ---> Not Digit

\\s ---> Space

\\S ---> Not Space

\\w ---> Word

\\W ---> Not Word

\\t ---> Tab

\\n ---> New line

^ ---> Beginning of the string

$ ---> End of the string

\ ---> Escape special characters, e.g. \\ is "\", \+ is "+"

| ---> Alternation match. e.g. /(e|d)n/ matches "en" and "dn"

• ---> Any character, except \n or line terminator

[ab] ---> a or b

[^ab] ---> Any character except a and b

[0-9] ---> All Digit

[A-Z] ---> All uppercase A to Z letters

[a-z] ---> All lowercase a to z letters

[A-z] ---> All Uppercase and lowercase a to z letters

i+i ---> at least one time

i*i ---> zero or more times

i?i ---> zero or 1 time

i{n}i ---> occurs n times in sequence

i{n1,n2}i ---> occurs n1 - n2 times in sequence

i{n1,n2}? ---> non greedy match, see above example

i{n,} ---> i occures >= n times

[:alnum:] ---> Alphanumeric characters: [:alpha:] and [:digit:]

[:alpha:] ---> Alphabetic characters: [:lower:] and [:upper:]

[:blank:] ---> Blank characters: e.g. space, tab

[:cntrl:] ---> Control characters

[:digit:] ---> Digits: 0 1 2 3 4 5 6 7 8 9

[:graph:] ---> Graphical characters: [:alnum:] and [:punct:]

[:lower:] ---> Lower-case letters in the current locale

[:print:] ---> Printable characters: [:alnum:], [:punct:] and space

[:punct:] --->Punctuation character: ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~

[:space:] ---> Space characters: tab, newline, vertical tab, form feed, carriage return, space

[:upper:] ---> Upper-case letters in the current locale

[:xdigit:] ---> Hexadecimal digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f