Functions, solutions

1. Write a function that divides two numbers. If the divider is zero, it shouldn’t try the division, but give a message about it.

my_first_function <- function(num1, num2){
  if (num2==0){
    stop("Not working")
}
  res <- num1/num2
  return(res)
}

2. Write a function that changes all vowels of a string to e-s.

esperente <- function(c){
  gsub("[aoiu]", "e", c)
}

3. Add a checking part, that checks if the input is indeed one character and it has vowels in it. If not, it should give a message.

esperente <- function(c){
  if (!is.character(c)){
    message("Not a character")
  }
  if (length(c)!=1){
    message("Too many elements!")
  }
  if (!grepl("[aoiu]", c)){
    message("The result will be the same!")
  }
  
  gsub("[aoiu]", "e", c)
}

4. Write a function that calculates the variance of a vector.

\[Var(x)=\frac 1{n-1}\sum_{i=1}^{n} (x_{i}-\overline{x})^2\] where \[\overline{x}=\frac{\sum_{i=1}^{n}x_{i}}n\]

variance <- function(num){
  
  sum((num-mean(num))^2)/(length(num)-1)
  
}

5. Add code to check if the input data is in the correct format.

variance <- function(num){
    if (!is.numeric(num))
    stop("The input can only be numeric.")
  if (length(num)<2){
    message("Calculating the variance only makes sense with more than two numbers!")
  }
  sum((num-mean(num))^2)/(length(num)-1)
  
}

6. Add a warning, if the class of the input vector is not numeric, and try to coerce as one.

variance <- function(num){
    if (!is.numeric(num))
      num <- as.numeric(num)
    warning("The input can only be numeric, tried to coerce as one.")
  if (length(num)<2){
    message("Calculating the variance only makes sense with more than two numbers!")
  }
  sum((num-mean(num))^2)/(length(num)-1)
  
}