CODEWITHSUNDEEP
rfunction
Rish
Rish

Reputation: 826

how to work backwards in a function in R

I was wondering if it would be possible to work backwards in a function in R in order to get a value for a variable that will output a known value.

For a simple example,

x<-5

afunction <- function(x,y) {
    x*y
}

How can I get the value of y that will output a known value of say 15. That is, I want the the return of the function to be 3.

Is this possible?

Thank you.

Upvotes: 2

Views: 204

Answers (1)

josliber
josliber

Reputation: 44340

If you are looking for the y value that makes afunction(x, y) equal 15, this is the same as finding the zeros of the following function:

g <- function(y) afunction(x, y) - 15

You can use uniroot to find zeros of a function:

uniroot(g, c(-100, 100))$root
# [1] 3

Note that you need to specify a range of y values for uniroot -- I've used [-100, 100] here.

Upvotes: 2

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