How to add a noise term in a formula

[melhzy]

I am trying to add a noise term in my formula, but I do not know how to make it happen.

For example, I have a function:

function_1 <- function(var1, var2, var3) {
  output <- (2*var1) + (-1*var2) + (3*var3)
  return(output)
}

But, I want to add a noise term in my formula like the following:

function_2 <- function(var1, var2, var3) {
  output <- (2*var1) + (-1*var2) + (3*var3) + noise
  return(output)
}

How could I make "function_2" in R properly? If any of you have any idea? I wanted to use the jitter function, but I am not sure if this may work or not.

function_2 <- function(var1, var2, var3) {
  output <- jitter((2*var1) + (-1*var2) + (3*var3))
  return(output)
}

Please let me know what do you guys think.

[martin.R]

This package may be overkill for your purposes, but it's worth checking:

GitHub - thomasp85/ambient: A Generator of Multidimensional Noise

[jim89]

If you're happy with random noise (i.e. random normals) you could use rnorm():

function_2 <- function(var1, var2, var3) {
  output <- (2*var1) + (-1*var2) + (3*var3) + rnorm(1, mean = 0, sd = 1)
  return(output)
}

You could use a different distribution to get random noise from if you wanted to, using the appropriate r[distribution-shorthand]() function instead of rnorm(), or change the mean and sd arguments to be something else, or control them with arguments to your function, too.

This is also assuming your var values are all length 1 (as opposed to vectors), if you're working with vectors you could add the normals afterwards, using the length of output to add a different amount of noise to each value:

function_2 <- function(var1, var2, var3) {
    output <- (2 * var1) + (-1 * var2) + (3 * var3)
    output + rnorm(length(output), mean = 0, sd = 1)
}

Or add the same amount of noise to each one, using the first example I gave above.

(Note that I didn't use return(), by default a function in R will return the last expression it evaluates).