Calling user inputs prompted through one R function in a second R function

Question

Thank you very much in advance for helping me out - I am new to R programming, and have got stuck with trying to use user-inputs accepted through one function within another. The second function is a simple pay calculator where the three variables are number of hours, per hour pay rate and the number of times the rate is multiplied once the number of working hours exceeds 180. I have written a first function called enterval through which I am asking the user to enter the above variables. In a second function called salary, I am trying to use enterval to accept the inputs before running the payout calculations. I am getting stuck because the second function, salary, is breaking when I come to an "if" condition, specifying if h > 180. I am sharing my code below. Thanks again for your kind assistance. I searched among previous answers but could not find a specific instance that fully answered my query - apologies if I missed out an appropriate previous response. The error I am getting on running this code is "Error in h > 180 : comparison (6) is possible only for atomic and list types"

enterval <- function()  {
h <- (readline("Please enter number of hours: "))
h <- as.integer(h)
r <- (readline("Please enter applicable rate: "))
r <- as.integer(r)
m <- (readline("Please confirm your multiplier: "))
m <- as.integer(m)
}
salary <- function ()  {
    enterval()
    if (h > 180)  {
        totalpay <- (180*r) + ((h-180)*r*m)
        }
    else  {
        totalpay <- (h*r)
        }
    totalpay
}

Answer 1

I think that what you need is the function to be like this:

enterval <- function()  {
  h <- (readline("Please enter number of hours: "))
  h <- as.numeric(h)
  r <- (readline("Please enter applicable rate: "))
  r <- as.numeric(r)
  m <- (readline("Please confirm your multiplier: "))
  m <- as.numeric(m)
  list(h=h, r=r, m=m)
}

salary <- function ()  {
  inputs <- enterval()
  if (inputs$h > 180)  {
    totalpay <- (180*inputs$r) + ((inputs$h-180)*inputs$r*inputs$m)
  }
  else  {
    totalpay <- (inputs$h*inputs$r)
  }
  totalpay
}

Output:

> salary()
Please enter number of hours: 5
Please enter applicable rate: 0.5
Please confirm your multiplier: 2
[1] 2.5

In your question, enterval just returned the value stored in m but even that was not saved anywhere (because you did not assign that to a variable inside salary so it could not be used by salary. In R functions return only the last object (or what the function return returns if used). In the function above I return a list with elements h, r and m.

Then I save that list to inputs which can be used by salary. Elements in inputs can be accessed using the $ operator.

Also, as a small addition, when you say rate I believe it is a number between 0-1 so I changed as.integer to as.numeric because as.integer will round down to the integer. Feel free to change that back to as.integer if indeed you needed an integer.

EDIT

Better and probably more advanced way of writing salary:

As per @RichardScriven 's comment a good way to avoid typing all the input$* variables is to use list2env like this:

salary <- function ()  {
  inputs <- enterval()
  list2env(inputs, environment())
  if (h > 180)  {
    totalpay <- (180*r) + (h-180)*r*m)
  }
  else  {
    totalpay <- (h*r)
  }
  totalpay
}

list2env will essentially create variables out of the list elements inside salary's environment, which are immediately accesible without needing to use input$*.

Answer 2

Variables assigned in R functions (similar to many other programming languages) have limited scope, this means that the m you assign in your function will only be available within that function. If you want your variable to be available outside of the function you have a two major options:

1. Return the variable, this is the preferred option, its much cleaner and is good programming practice for numerous reasons described in many stack overflow post. An important thing to remember is a function can only return one variable.

2. You can do a global assignment, this will make the variable in your function have a global scope and be accessible within all functions. The code for this is m <<- 1 as opposed to m <- 1. This isn't recommended for a variety of reasons. See Global variables in R or Global and local variables in R for more on this subject.

Since you can only return one variable you might put all three objects into a data frame or a list and return that. Though I would question whether you want the value entry done in a function. Additionally if you're user input is primary to your goal R might not be the right language. That being said the code below accomplishes what you're looking for

enterval <- function()  {
  h <- (readline("Please enter number of hours: "))
  h <- as.integer(h)
  r <- (readline("Please enter applicable rate: "))
  r <- as.integer(r)
  m <- (readline("Please confirm your multiplier: "))
  m <- as.integer(m)
  salaryVariables <- data.frame("hours" = h, "rate" = r, "multiplier" = m)
  return(salaryVariables)
}
salary <- function(salaryInfo)  {
  r <- salaryInfo$rate
  h <- salaryInfo$hours
  m <- salaryInfo$multiplier
  if (h > 180)  {
    totalpay <- (180*r) + ((h-180)*r*m)
  }
  else  {
    totalpay <- (h*r)
  }
  return(totalpay)
}

mySalary <- enterval()
salary(mySalary)