Section 8 Error Message

8.1 Condition

Condition	Explanation
message	A generic notification/diagnostic message produced by the message() function; execution of the function continues.
warning	An indication that something is wrong but not necessarily fatal; execution of the function continues. Warnings are generated by the warning() function.
error	An indication that a fatal problem has occurred and execution of the function stops. Errors are produced by the stop() function.

8.2 Example 1

sqrt(4)

sqrt(-4)

sqrt('A')

8.3 Example 2

printMsg <- function(x) {
  if(x > 0){
    msg <- paste0(x, ' is a positive number')
  } else {
    msg <- paste0(x, ' is a negative number')
  }
  print(msg)
}

printMsg(5)

printMsg(-5)

printMsg(0)

printMsg(NA)

8.4 Example 3

printMsg <- function(x) {
  if(is.na(x)){
    msg <- paste0('Encountered a missing value')
  } else if (x == 0) {
    msg <- paste0(x, ' is neither a positive nor a negative number')
  } else if (x > 0) {
    msg <- paste0(x, ' is a positive number')
  } else if (x < 0) {
    msg <- paste0(x, ' is a negative number')
  }
  print(msg)
}

printMsg(5)

printMsg(-5)

printMsg(0)

printMsg(NA)

printMsg(c(5, -10, NA))

8.5 Example 4

printMsg <- function(x) {
  
  msg <- NULL
  
  if(length(x) > 1){
    stop('x should be of length 1')
  } else if(is.na(x)){
    warning('Encountered a missing value')
  } else if (x == 0) {
    msg <- paste0(x, ' is neither a positive nor a negative number')
  } else if (x > 0) {
      msg <- paste0(x, ' is a positive number')
  } else if (x < 0) {
      msg <- paste0(x, ' is a negative number')
  }
  
  if(!is.null(msg)) print(msg)

}

printMsg(5)

printMsg(-5)

printMsg(0)

printMsg(NA)

printMsg(c(0, 5, -10, NA))

8.6 Example 5

Vectorize creates a function wrapper that vectorizes the action of its argument FUN.

printMsgNew <- function(x) {
  
  msg <- NULL
  
  if(is.na(x)){
      msg <- 'Encountered a missing value'
  } else if (x == 0) {
      msg <- paste0(x, ' is neither a positive nor a negative number')
  } else if (x > 0) {
      msg <- paste0(x, ' is a positive number')
  } else if (x < 0) {
      msg <- paste0(x, ' is a negative number')
  }
  
  if(!is.null(msg)) print(msg)

}

printMessageVec <- Vectorize(printMsgNew)

out <- printMessageVec(c(-5,0,5,NA))

8.7 Common error messages

• Error: could not find function

• Error in if function: missing value where TRUE/FALSE is needed

• Error: Error in eval; object not found

• Error: cannot open the connection

• Error: incorrect number of dimensions

• Error: subscript out of bounds

• Error: undefined columns selected

• Error: non-numeric argument to a binary operator

• Error: no applicable method - caused by using an object-oriented function on a data type it does not support