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Basic string manipulation typically inludes case conversion, simple character, abbreviating, substring replacement, adding/removing whitespace, and performing set operations to compare similarities and differences between two character vectors. These operations can all be performed with base R functions; however, some operations (or at least their syntax) are greatly simplified with the stringr package. This section illustrates base R string manipulation for case conversion, simple character replacement, abbreviating, and substring replacement. Many of the other fundamental string manipulation tasks will be covered in the String manipulation with stringr and Set operatons for character strings tutorials.
To convert all upper case characters to lower case use tolower():
x <- "Learning To MANIPULATE strinGS in R"
tolower(x)
## [1] "learning to manipulate strings in r"
To convert all lower case characters to upper case use toupper():
toupper(x)
## [1] "LEARNING TO MANIPULATE STRINGS IN R"
To replace a character (or multiple characters) in a string you can use chartr():
# replace 'A' with 'a'
x <- "This is A string."
chartr(old = "A", new = "a", x)
## [1] "This is a string."
# multiple character replacements
# replace any 'd' with 't' and any 'z' with 'a'
y <- "Tomorrow I plzn do lezrn zbout dexduzl znzlysis."
chartr(old = "dz", new = "ta", y)
## [1] "Tomorrow I plan to learn about textual analysis."
Note that chartr() replaces every identified letter for replacement so the only time I use it is when I am certain that I want to change every possible occurence of a letter.
To abbreviate strings you can use abbreviate():
streets <- c("Main", "Elm", "Riverbend", "Mario", "Frederick")
# default abbreviations
abbreviate(streets)
## Main Elm Riverbend Mario Frederick
## "Main" "Elm" "Rvrb" "Mari" "Frdr"
# set minimum length of abbreviation
abbreviate(streets, minlength = 2)
## Main Elm Riverbend Mario Frederick
## "Mn" "El" "Rv" "Mr" "Fr"
Note that if you are working with U.S. states, R already has a pre-built vector with state names (state.name). Also, there is a pre-built vector of abbreviated state names (state.abb).
To extract or replace substrings in a character vector there are three primary base R functions to use: substr(), substring(), and strsplit(). The purpose of substr() is to extract and replace substrings with specified starting and stopping characters:
alphabet <- paste(LETTERS, collapse = "")
# extract 18th character in string
substr(alphabet, start = 18, stop = 18)
## [1] "R"
# extract 18-24th characters in string
substr(alphabet, start = 18, stop = 24)
## [1] "RSTUVWX"
# replace 1st-17th characters with `R`
substr(alphabet, start = 19, stop = 24) <- "RRRRRR"
alphabet
## [1] "ABCDEFGHIJKLMNOPQRRRRRRRYZ"
The purpose of substring() is to extract and replace substrings with only a specified starting point. substring() also allows you to extract/replace in a recursive fashion:
alphabet <- paste(LETTERS, collapse = "")
# extract 18th through last character
substring(alphabet, first = 18)
## [1] "RSTUVWXYZ"
# recursive extraction; specify start position only
substring(alphabet, first = 18:24)
## [1] "RSTUVWXYZ" "STUVWXYZ" "TUVWXYZ" "UVWXYZ" "VWXYZ" "WXYZ"
## [7] "XYZ"
# recursive extraction; specify start and stop positions
substring(alphabet, first = 1:5, last = 3:7)
## [1] "ABC" "BCD" "CDE" "DEF" "EFG"
To split the elements of a character string use strsplit():
z <- "The day after I will take a break and drink a beer."
strsplit(z, split = " ")
## [[1]]
## [1] "The" "day" "after" "I" "will" "take" "a" "break"
## [9] "and" "drink" "a" "beer."
a <- "Alabama-Alaska-Arizona-Arkansas-California"
strsplit(a, split = "-")
## [[1]]
## [1] "Alabama" "Alaska" "Arizona" "Arkansas" "California"
Note that the output of strsplit() is a list. To convert the output to a simple atomic vector simply wrap in unlist():
unlist(strsplit(a, split = "-"))
## [1] "Alabama" "Alaska" "Arizona" "Arkansas" "California"