R Programming: Learn To Manipulate Strings In R

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Slide 1 www.r-squared.in/rprogramming
R Programming
Learn the fundamentals of data analysis with R.

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Course Modules
www.r-squared.in/rprogramming
✓ Introduction
✓ Elementary Programming
✓ Working With Data
✓ Selection Statements
✓ Loops
✓ Functions
✓ Debugging
✓ Unit Testing

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Working With Data
✓ Data Types
✓ Data Structures
✓ Data Creation
✓ Data Info
✓ Data Subsetting
✓ Comparing R Objects
✓ Importing Data
✓ Exporting Data
✓ Data Transformation
✓ Numeric Functions
✓ String Functions
✓ Mathematical Functions

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In this unit, we will explore string manipulation in R using the following functions:
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String Functions
● match()
● char.expand()
● grep()
● grepl()
● sub()
● substr()
● substring()
● strsplit()
● strtrim()
● chartr()
● tolower()
● toupper()
● toString()
● nchar()
● nzchar()
● noquote()
● pmatch()
● charmatch()

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chartr()
Description
chartr() replaces characters in a string.
Syntax
chartr(old, new, x)
Returns
String with replaced characters
Documentation
help(chartr)

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chartr()
Examples
> # example 1
> name <- "Jovial Mann"
> chartr("J", "K", name)
[1] "Kovial Mann"
> # example 2
> chartr("a", "e", name)
[1] "Joviel Menn"

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tolower()/toupper()
Description
tolower() translates characters from upper to lower case.
toupper() translates characters from lower to upper case.
Syntax
tolower(x)
toupper(x
Returns
String translated to lower or upper case
Documentation
help(tolower)
help(toupper)

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tolower()/toupper()
Examples
> # example 1
> tolower(name)
[1] "jovial mann"
> # example 2
> tolower(name)
[1] "jovial mann"
> toupper(name)
[1] "JOVIAL MANN"

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toString()
Description
toString() converts an R object to character string.
Syntax
toString(x)
Returns
Character vector of length 1
Documentation
help(toString)

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toString()
Examples
> example 1
> x <- 100
> toString(x)
[1] "100"
> name <- c("Jovial", "Mann")
> name
[1] "Jovial" "Mann"
> toString(name)
[1] "Jovial, Mann"
> toString(name, width = 8)
[1] "Jovi...."
[1] "Jovial, Mann"
[1] "Jo...."

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nchar()
Description
nchar() returns the size of character strings. It takes a character vector as argument and
returns a vector that contains the size of the elements of the argument.
Syntax
nchar(character vector)
Returns
Integer vector
Documentation
help(nchar)

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nchar()
Examples
> # example 1
> nchar(name)
[1] 6 4
> first_name <- "Jovial"
> nchar("first_name")
[1] 10
> last_name <- "Mann"
> nchar(last_name)
[1] 4

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nzchar()
Description
nzchar() tests whether elements of a character vector are non-empty strings.
Syntax
nzchar(character vector)
Returns
Logical vector
Documentation
help(nzchar)

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nzchar()
Examples
> # example 1
> nzchar(name)
[1] TRUE TRUE
> # example 2
> details <- c("Jovial", "")
> nzchar(details)
[1] TRUE FALSE

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noquote()
Description
noquote() returns character strings without quotes.
Syntax
noquote(object)
Returns
Character strings without quotes
Documentation
help(noquote)

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noquote()
Examples
> # example 1
> letters
[1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v"
[23] "w" "x" "y" "z"
> nql <- noquote(letters)
> nql
[1] a b c d e f g h i j k l m n o p q r s t u v w x y z

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pmatch()
Description
pmatch() performs partial string matching. It takes two arguments and seeks matches for
the elements of the first argument in the second.
Syntax
pmatch(x, table)
Returns
Integer vector indicating index of elements that have a match
Documentation
help(pmatch)

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pmatch()
Examples
> # example
> pmatch("Jov", c("Jovial", "Jovathon", "John"))
[1] NA
> pmatch("Jovi", c("Jovial", "Jovathon", "John"))
[1] 1
> pmatch("m", c("mean", "median", "mode"))
[1] NA
> pmatch("med", c("mean", "median", "mode"))
[1] 2

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charmatch()
Description
charmatch() performs partial string matching. It takes two arguments and seeks matches
for the elements of the first argument in the second.
Syntax
charmatch(x, table)
Returns
Integer vector indicating index of elements that have a match
Documentation
help(charmatch)

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charmatch()
Examples
> # example 1
> charmatch("Jov", c("Jovial", "Jovathon", "John"))
[1] 0
> charmatch("Jovi", c("Jovial", "Jovathon", "John"))
[1] 1
> charmatch("m", c("mean", "median", "mode"))
[1] 0
> charmatch("med", c("mean", "median", "mode"))
[1] 2

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match()
Description
match() takes 2 arguments and returns the index of the character element in the second
argument that matches the first one.
Syntax
match(x, table)
Returns
Integer vector of characters that match
Documentation
help(match)

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match()
Examples
> # example 1
> x <- sample(1:10)
> x
[1] 9 8 3 7 1 5 10 2 6 4
> match(5, x)
[1] 6
> # example 2
> x <- sample(letters)
> x
[1] "t" "e" "i" "b" "h" "g" "c" "q" "u" "s" "r" "z" "j" "v" "y" "k" "l" "w" "p" "m" "d" "a"
[23] "f" "x" "o" "n"
> match("a", x)
[1] 22

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char.expand()
Description
char.expand() takes two arguments and seeks match for the first argument in the
elements of its second argument and returns the element if a match is found.
Syntax
char.expand(input, target)
Returns
Element in target that is a match for input.
Documentation
help(char.expand)

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char.expand()
Examples
> # example 1
> loc <- c("mean", "median", "mode")
> char.expand("me", loc, nomatch = stop("no match"))
character(0)
> char.expand("mo", loc)
[1] "mode"
> char.expand("med", loc)
[1] "median"

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grep()
Description
grep() takes two arguments and seeks match for the first argument in the elements of its
second argument and returns the index of the elements that match.
Syntax
grep(pattern, character vector)
Returns
Integer vector indicating the index of elements in the character vector that match the
pattern
Documentation
help(grep)

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grep()
Examples
> # example 1
> grep("a", c("mean", "median", "mode"))
[1] 1 2
> grep("d", c("mean", "median", "mode"))
[1] 2 3
> grep("me", c("mean", "median", "mode"))
[1] 1 2
> grep("od", c("mean", "median", "mode"))
[1] 3

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grepl()
Description
grepl() takes two arguments and seeks match for the first argument in the elements of its
second argument and returns a logical vector if there is a match
Syntax
grepl(pattern, character vector)
Returns
Logical vector
Documentation
help(grepl)

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grepl()
Examples
> # example 1
> grepl("a", c("mean", "median", "mode"))
[1] TRUE TRUE FALSE
> grepl("d", c("mean", "median", "mode"))
[1] FALSE TRUE TRUE
> grepl("me", c("mean", "median", "mode"))
[1] TRUE TRUE FALSE
> grepl("od", c("mean", "median", "mode"))#
[1] FALSE FALSE TRUE

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sub()
Description
sub() takes three arguments and seeks match for the first argument in the elements of its
third argument and replaces them with the second argument.
Syntax
sub(pattern, replacement, character vector)
Returns
Character vector with replaced string
Documentation
help(sub)

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sub()
Examples
> # example 1
> str <- "Good Morning"
> sub("Go", "Mo", str)
[1] "Mood Morning"
> # example 2
> str <- c("mean", "median", "mode" )
> sub("m", "k", str)
[1] "kean" "kedian" "kode"

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substr()
Description
substr() extracts or replaces substring in a character vector.
Syntax
substr(character vector, start, stop)
Returns
Substring or character vector with replaced substring
Documentation
help(substr)

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substr()
Examples
> # example 1
> substr("abcdef", 2, 4)
[1] "bcd"
> # example 2
> substr("abcdef", 2, 4)
[1] "bcd"
> substr(rep("abcdef", 4), 1:4, 4:5)
[1] "abcd" "bcde" "cd" "de"
> x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
> substr(x, 2, 5)
[1] "sfef" "wert" "uiop" "" "tuff"

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substring()
Description
substring() extracts or replaces substring in a character vector.
Syntax
substr(character vector, first, last)
Returns
Substring or character vector with replaced substring
Documentation
help(substring)

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substring()
Examples
> # example 1
> substring("abcdef", 1, 1:6)
[1] "a" "ab" "abc" "abcd" "abcde" "abcdef"
> x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
> substring(x, 2, 4:6)
[1] "sfe" "wert" "uiop[" "" "tuff"
> substring(x, 2) <- c("..", "+++")
> x
[1] "a..ef" "q+++ty" "y..op[" "b" "s..ff.blah.yech"

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strsplit()
Description
strsplit() takes two arguments and splits the elements of the first argument at the index
position of the second argument if the characters in the first argument match the secon
argument.
Syntax
strsplit(character vector, split)
Returns
List of elements in the first argument split by the second argument.
Documentation
help(strsplit)

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strsplit()
Examples
> # example 1
> x <- c(as = "asfef", qu = "qwerty", "yuiop[", "b", "stuff.blah.yech")
> x
as qu
"asfef" "qwerty" "yuiop[" "b" "stuff.blah.yech"
> strsplit(x, "e")
$as
[1] "asf" "f"
$qu
[1] "qw" "rty"
[[3]]
[1] "yuiop["
[[4]]
[1] "b"
[[5]]
[1] "stuff.blah.y" "ch"

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strsplit()
Examples
> # example 2
> y <- c("India", "America", "Australia", "China", "Russia", "Britain")
> strsplit(y, "i")
[[1]]
[1] "Ind" "a"
[[2]]
[1] "Amer" "ca"
[[3]]
[1] "Austral" "a"
[[4]]
[1] "Ch" "na"
[[5]]
[1] "Russ" "a"
[[6]]
[1] "Br" "ta" "n"

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strtrim()
Description
strtrim() takes two arguments and trims the first argument at the index mentioned in the
second argument.
Syntax
strtrim(character vector, index)
Returns
Trimmed character vector
Documentation
help(strtrim)

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strtrim()
Examples
> # example 1
> name
[1] "Jovial" "Mann"
> strtrim(name, 4)
[1] "Jovi" "Mann"
> # example 2
> alphabets <- "aksjdnfkasdjhfkjasdkfalkdsfnkajdsnfkjadn"
> strtrim(alphabets, 10)
[1] "aksjdnfkas"

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In the next unit, we will explore the following mathematical functions:
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Next Steps...
● abs()
● round()
● ceiling()
● floor()
● trunc()
● signif()
● jitter()
● format()
● formatC()

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R Programming: Learn To Manipulate Strings In R

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