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Dealing with character strings is often under-emphasized in data analysis training. The focus typically remains on numeric values; however, the growth in data collection is also resulting in greater bits of information embedded in character strings. Consequently, handling, cleaning and processing character strings is becoming a prerequisite in daily data analysis. In this section you’ll learn the basics of creating, converting and printing character strings followed by how to count the number of elements and characters in a string.
The most basic way to create strings is to use quotation marks and assign a string to an object similar to creating number sequences.
a <- "learning to create" # create string a
b <- "character strings" # create string b
The paste() function provides a versatile means for creating and building strings. It takes one or more R objects, converts them to “character”, and then it concatenates (pastes) them to form one or several character strings.
# paste together string a & b
paste(a, b)
## [1] "learning to create character strings"
# paste character and number strings (converts numbers to character class)
paste("The life of", pi)
## [1] "The life of 3.14159265358979"
# paste multiple strings
paste("I", "love", "R")
## [1] "I love R"
# paste multiple strings with a separating character
paste("I", "love", "R", sep = "-")
## [1] "I-love-R"
# use paste0() to paste without spaces btwn characters
paste0("I", "love", "R")
## [1] "IloveR"
# paste objects with different lengths
paste("R", 1:5, sep = " v1.")
## [1] "R v1.1" "R v1.2" "R v1.3" "R v1.4" "R v1.5"
Test if strings are characters with is.character() and convert strings to character with as.character() or with toString().
a <- "The life of"
b <- pi
is.character(a)
## [1] TRUE
is.character(b)
## [1] FALSE
c <- as.character(b)
is.character(c)
## [1] TRUE
toString(c("Aug", 24, 1980))
## [1] "Aug, 24, 1980"
The common printing methods include:
print(): generic printingnoquote(): print with no quotescat(): concatenate and print with no quotessprintf(): a wrapper for the C function sprintf, that returns a character vector containing a formatted combination of text and variable valuesThe primary printing function in R is print()
x <- "learning to print strings"
# basic printing
print(x)
## [1] "learning to print strings"
# print without quotes
print(x, quote = FALSE)
## [1] learning to print strings
An alternative to printing a string without quotes is to use noquote()
noquote(x)
## [1] learning to print strings
Another very useful function is cat() which allows us to concatenate objects and print them either on screen or to a file. The output result is very similar to noquote(); however, cat() does not print the numeric line indicator. As a result, cat() can be useful for printing nicely formated responses to users.
# basic printing (similar to noquote)
cat(x)
## learning to print strings
# combining character strings
cat(x, "in R")
## learning to print strings in R
# basic printing of alphabet
cat(letters)
## 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
# specify a seperator between the combined characters
cat(letters, sep = "-")
## 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
# collapse the space between the combine characters
cat(letters, sep = "")
## abcdefghijklmnopqrstuvwxyz
You can also format the line width for printing long strings using the fill argument:
x <- "Today I am learning how to print strings."
y <- "Tomorrow I plan to learn about textual analysis."
z <- "The day after I will take a break and drink a beer."
cat(x, y, z, fill = 0)
## Today I am learning how to print strings. Tomorrow I plan to learn about textual analysis. The day after I will take a break and drink a beer.
cat(x, y, z, fill = 5)
## Today I am learning how to print strings.
## Tomorrow I plan to learn about textual analysis.
## The day after I will take a break and drink a beer.
sprintf() is a useful printing function for precise control of the output. It is a wrapper for the C function sprintf and returns a character vector containing a formatted combination of text and variable values.
To substitute in a string or string variable, use %s:
x <- "print strings"
# substitute a single string/variable
sprintf("Learning to %s in R", x)
## [1] "Learning to print strings in R"
# substitute multiple strings/variables
y <- "in R"
sprintf("Learning to %s %s", x, y)
## [1] "Learning to print strings in R"
For integers, use %d or a variant:
version <- 3
# substitute integer
sprintf("This is R version:%d", version)
## [1] "This is R version:3"
# print with leading spaces
sprintf("This is R version:%4d", version)
## [1] "This is R version: 3"
# can also lead with zeros
sprintf("This is R version:%04d", version)
## [1] "This is R version:0003"
For floating-point numbers, use %f for standard notation, and %e or %E for exponential notation:
sprintf("%f", pi) # '%f' indicates 'fixed point' decimal notation
## [1] "3.141593"
sprintf("%.3f", pi) # decimal notation with 3 decimal digits
## [1] "3.142"
sprintf("%1.0f", pi) # 1 integer and 0 decimal digits
## [1] "3"
sprintf("%5.1f", pi) # decimal notation with 5 total decimal digits and
## [1] " 3.1" # only 1 to the right of the decimal point
sprintf("%05.1f", pi) # same as above but fill empty digits with zeros
## [1] "003.1"
sprintf("%+f", pi) # print with sign (positive)
## [1] "+3.141593"
sprintf("% f", pi) # prefix a space
## [1] " 3.141593"
sprintf("%e", pi) # exponential decimal notation 'e'
## [1] "3.141593e+00"
sprintf("%E", pi) # exponential decimal notation 'E'
## [1] "3.141593E+00"
To count the number of elements in a string use length():
length("How many elements are in this string?")
## [1] 1
length(c("How", "many", "elements", "are", "in", "this", "string?"))
## [1] 7
To count the number of characters in a string use nchar():
nchar("How many characters are in this string?")
## [1] 39
nchar(c("How", "many", "characters", "are", "in", "this", "string?"))
## [1] 3 4 10 3 2 4 7