R – Keywords

R is an open-source programming language that is widely used as a statistical software and data analysis tool. R generally comes with the Command-line interface. R is available across widely used platforms like Windows, Linux, and macOS. Also, the R programming language is the latest cutting-edge tool.

Keywords are specific reserved words in R, each of which has a specific feature associated with it. Almost all of the words which help one to use the functionality of the R language are included in the list of keywords. So one can imagine that the list of keywords is not going to be a small one! In R, one can view these keywords by using either help(reserved) or ?reserved. Here is the list of keywords in R:

if

else

while

repeat

for

function

in

next

break

TRUE

FALSE

NULL

Inf

NaN

NA

NA_integer

NA_real

NA_complex_

NA_character_

…

Following are some most important keywords along with their examples:

• if: If statement is one of the Decision-making statements in the R programming language. It is one of the easiest decision-making statements. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statement is executed otherwise not.
  Example:

  # R program to illustrate if statement
  
  # assigning value to variable a
  a <- 5
  
  # condition
  if( a > 0 )
  {
      print("Positive Number") # Statement
  }

  Output:

  Positive Number
  

• else: It is similar to if statement but when the test expression in if condition fails, then statements in else condition are executed.
  Example:

  x <- 5
  
  # Check value is less than or greater than 10
  if(x > 10)
  {
      print(paste(x, "is greater than 10"))
  }
  else
  {
      print(paste(x, "is less than 10"))
  }

  Output:

  [1] "5 is less than 10"
  

• while: It is a type of control statement which will run a statement or a set of statements repeatedly unless the given condition becomes false. It is also an entry controlled loop, in this loop the test condition is tested first, then the body of the loop is executed, the loop body would not be executed if the test condition is false.
  Example:

  # R program to demonstrate the use of while loop
  
  val = 1
  
  # using while loop
  while (val <= 5 )
  {
      # statements
      print(val)
      val = val + 1
  }

  Output:

  [1] 1
  [1] 2
  [1] 3
  [1] 4
  [1] 5
  

• repeat: It is a simple loop that will run the same statement or a group of statements repeatedly until the stop condition has been encountered. Repeat loop does not have any condition to terminate the loop, a programmer must specifically place a condition within the loop’s body and use the declaration of a break statement to terminate this loop. If no condition is present in the body of the repeat loop then it will iterate infinitely.
  Example:

  # R program to demonstrate the use of repeat loop
  
  val = 1
  
  # using repeat loop
  repeat
  {
      # statements
      print(val)
      val = val + 1
  
      # checking stop condition
      if(val > 5)
      {
          # using break statement
          # to terminate the loop
          break
      }
  }

  Output:

  [1] 1
  [1] 2
  [1] 3
  [1] 4
  [1] 5
  

• for: It is a type of control statement that enables one to easily construct a loop that has to run statements or a set of statements multiple times. For loop is commonly used to iterate over items of a sequence. It is an entry controlled loop, in this loop the test condition is tested first, then the body of the loop is executed, the loop body would not be executed if the test condition is false.
  Example:

  # R program to demonstrate the use of for loop
  
  # using for loop
  for (val in 1:5)
  {
      # statement
      print(val)
  }

  Output:

  [1] 1
  [1] 2
  [1] 3
  [1] 4
  [1] 5
  

• function: Functions are useful when you want to perform a certain task multiple number of times. In R functions are created using function keyword.
  Example:

  # A simple R function to check
  # whether x is even or odd
  
  evenOdd = function(x){
  if(x %% 2 == 0)
      return("even")
  else
      return("odd")
  }
  
  print(evenOdd(4))
  print(evenOdd(3))

  Output:

  [1] "even"
  [1] "odd"
  

• next:Next statement in R is used to skip any remaining statements in the loop and continue the execution of the program. In other words, it is a statement that skips the current iteration without loop termination.
  Example:

  # R program to illustrate next in for loop
  
  val <- 6:11
  
  # Loop
  for (i in val)
  {
      if (i == 8)
      {
          # test expression
          next
      }
      print(i)
  }

  Output:

  [1] 6
  [1] 7
  [1] 9
  [1] 10
  [1] 11
  

• break: The break keyword is a jump statement that is used to terminate the loop at a particular iteration.
  Example:

  # R Break Statement Example
  a<-1
  while (a < 10)
  {
      print(a)
      if(a == 5)
          break
      a = a + 1
  }

  Output:

  [1] 1
  [1] 2
  [1] 3
  [1] 4
  [1] 5
  

• TRUE/FALSE: The TRUE and FALSE keywords are used to represent a Boolean true and Boolean false. If the given statement is true, then the interpreter returns true else the interpreter returns false.
  Example:

  # A simple R program
  # to illustrate TRUE / FALSE
  
  # Sample values
  x = 4
  y = 3
  
  # Comparing two values
  z = x > y
  p = x < y
  
  # print the logical value
  print(z)
  print(p)

  Output:

  [1] TRUE
  [1] FALSE
  

• NULL: In R, NULL represents the null object. NULL is used to represent missing and undefined values. NULL is the logical representation of a statement which is neither TRUE nor FALSE.
  Example:

  # A simple R program
  # to illustrate NULL
  
  v = as.null(c(1, 2, 3, 4))
  print(v)

  Output:

  NULL
  

• Inf and NaN: In R is.finite and is.infinite return a vector of the same length as x, where x is an R object to be tested. This indicating which elements are finite (not infinite and not missing) or infinite. Inf and -Inf keyword mean positive and negative infinity whereas NaN keyword means ‘Not a Number’.

  # A simple R program
  # to illustrate Inf and NaN
  
  # To check Inf
  x = c(Inf, 2, 3)
  print(is.finite(x))
  
  # To check NaN
  y = c(1, NaN, 3)
  print(is.nan(y))

  Output:

  [1] FALSE  TRUE  TRUE
  [1] FALSE  TRUE FALSE
  

• NA: NA stands for “Not Available” and is used to represent missing values. There are also constants NA_integer_, NA_real_, NA_complex_ and NA_character_ of the other atomic vector types which support missing values and all of these are reserved words in the R language.

  # A simple R program
  # to illustrate  NA
  
  # To check NA
  x = c(1, NA, 2, 3)
  print(is.na(x))

  Output:

  [1] FALSE  TRUE FALSE FALSE