R - Strings


Advertisements


Any value written within a pair of single quote or double quotes in R is treated as a string. Internally R stores every string within double quotes, even when you create them with single quote.

Rules Applied in String Construction

  • The quotes at the beginning and end of a string should be both double quotes or both single quote. They can not be mixed.

  • Double quotes can be inserted into a string starting and ending with single quote.

  • Single quote can be inserted into a string starting and ending with double quotes.

  • Double quotes can not be inserted into a string starting and ending with double quotes.

  • Single quote can not be inserted into a string starting and ending with single quote.

Examples of Valid Strings

Following examples clarify the rules about creating a string in R.

a <- 'Start and end with single quote'
print(a)

b <- "Start and end with double quotes"
print(b)

c <- "single quote ' in between double quotes"
print(c)

d <- 'Double quotes " in between single quote'
print(d)

When the above code is run we get the following output −

[1] "Start and end with single quote"
[1] "Start and end with double quotes"
[1] "single quote ' in between double quote"
[1] "Double quote \" in between single quote"

Examples of Invalid Strings

e <- 'Mixed quotes" 
print(e)

f <- 'Single quote ' inside single quote'
print(f)

g <- "Double quotes " inside double quotes"
print(g)

When we run the script it fails giving below results.

Error: unexpected symbol in:
"print(e)
f <- 'Single"
Execution halted

String Manipulation

Concatenating Strings - paste() function

Many strings in R are combined using the paste() function. It can take any number of arguments to be combined together.

Syntax

The basic syntax for paste function is −

paste(..., sep = " ", collapse = NULL)

Following is the description of the parameters used −

  • ... represents any number of arguments to be combined.

  • sep represents any separator between the arguments. It is optional.

  • collapse is used to eliminate the space in between two strings. But not the space within two words of one string.

Example

a <- "Hello"
b <- 'How'
c <- "are you? "

print(paste(a,b,c))

print(paste(a,b,c, sep = "-"))

print(paste(a,b,c, sep = "", collapse = ""))

When we execute the above code, it produces the following result −

[1] "Hello How are you? "
[1] "Hello-How-are you? "
[1] "HelloHoware you? "

Formatting numbers & strings - format() function

Numbers and strings can be formatted to a specific style using format() function.

Syntax

The basic syntax for format function is −

format(x, digits, nsmall, scientific, width, justify = c("left", "right", "centre", "none")) 

Following is the description of the parameters used −

  • x is the vector input.

  • digits is the total number of digits displayed.

  • nsmall is the minimum number of digits to the right of the decimal point.

  • scientific is set to TRUE to display scientific notation.

  • width indicates the minimum width to be displayed by padding blanks in the beginning.

  • justify is the display of the string to left, right or center.

Example

# Total number of digits displayed. Last digit rounded off.
result <- format(23.123456789, digits = 9)
print(result)

# Display numbers in scientific notation.
result <- format(c(6, 13.14521), scientific = TRUE)
print(result)

# The minimum number of digits to the right of the decimal point.
result <- format(23.47, nsmall = 5)
print(result)

# Format treats everything as a string.
result <- format(6)
print(result)

# Numbers are padded with blank in the beginning for width.
result <- format(13.7, width = 6)
print(result)

# Left justify strings.
result <- format("Hello", width = 8, justify = "l")
print(result)

# Justfy string with center.
result <- format("Hello", width = 8, justify = "c")
print(result)

When we execute the above code, it produces the following result −

[1] "23.1234568"
[1] "6.000000e+00" "1.314521e+01"
[1] "23.47000"
[1] "6"
[1] "  13.7"
[1] "Hello   "
[1] " Hello  "

Counting number of characters in a string - nchar() function

This function counts the number of characters including spaces in a string.

Syntax

The basic syntax for nchar() function is −

nchar(x)

Following is the description of the parameters used −

  • x is the vector input.

Example

result <- nchar("Count the number of characters")
print(result)

When we execute the above code, it produces the following result −

[1] 30

Changing the case - toupper() & tolower() functions

These functions change the case of characters of a string.

Syntax

The basic syntax for toupper() & tolower() function is −

toupper(x)
tolower(x)

Following is the description of the parameters used −

  • x is the vector input.

Example

# Changing to Upper case.
result <- toupper("Changing To Upper")
print(result)

# Changing to lower case.
result <- tolower("Changing To Lower")
print(result)

When we execute the above code, it produces the following result −

[1] "CHANGING TO UPPER"
[1] "changing to lower"

Extracting parts of a string - substring() function

This function extracts parts of a String.

Syntax

The basic syntax for substring() function is −

substring(x,first,last)

Following is the description of the parameters used −

  • x is the character vector input.

  • first is the position of the first character to be extracted.

  • last is the position of the last character to be extracted.

Example

# Extract characters from 5th to 7th position.
result <- substring("Extract", 5, 7)
print(result)

When we execute the above code, it produces the following result −

[1] "act"


Advertisements