R: How to use current function output's within this function

Question

I write a R function using if & else if in it. See the code below:

i_ti_12 <- function(x){
  if (x <= 44)
  {ti = exp(-13.2238 + 0.152568*x)}
  else if (x >= 49)
  {ti = -0.01245109 + 0.000315605*x}
  else (x > 44 & x < 49)
  {ti = (x-44)*(i_ti_12(49))/(49-44) + (49-x)*(i_ti_12(44))/(49-44)}
  return(ti)
}

I want to use this function's output, i_ti_12(49) within this function, but the above code doesn't work. The output is:

> i_ti_12(49)
Error: C stack usage  7974292 is too close to the limit

The simple solution is just replace i_ti_12(49) by -0.01245109 + 0.000315605*49, but its not a clear way to solve it and might not work in complex cases.

So I really want to know and to learn if there are clear methods to do this? I mean, like above simple example, write a conditional function using one condition's output in this function. Any help is highly appreciate.

ThomasIsCoding · Accepted Answer · 2020-02-19 11:25:59Z

2

Your last else is followed by a condition (x > 44 & x < 49), which actually is not correct. If you have (x > 44 & x < 49) there, that means you will execute that statement, and ti = (x-44)*(i_ti_12(49))/(49-44) + (49-x)*(i_ti_12(44))/(49-44) is something independent with your if-else structure.

In that case, when you call i_ti_12(49), your function does not know when the recursion should be terminated since you did not define that case.

You can try the code below:

i_ti_12 <- function(x){
  if (x <= 44)
  {ti = exp(-13.2238 + 0.152568*x)}
  else if (x >= 49)
  {ti = -0.01245109 + 0.000315605*x}
  else
  {ti = (x-44)*(i_ti_12(49))/(49-44) + (49-x)*(i_ti_12(44))/(49-44)}
  return(ti)
}

such that

> i_ti_12(49)
[1] 0.003013555

edited Feb 19, 2020 at 11:25

answered Feb 19, 2020 at 11:16

ThomasIsCoding

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4 Comments

Hillary Over a year ago

Wow! It works! Could you explain why it works after removing the final condition?

ThomasIsCoding Over a year ago

@Hillary see some of my explanation, hope it is helpful

Hillary Over a year ago

@ThomaslsCoding This makes sense! Thanks a lot! Do you know why R function is so clear that it can recognize its conditional output? In this case, does R function run the first condition and save the return(ti) and then run the second condition and save the corresponding return, and then to the third condition?

ThomasIsCoding Over a year ago

@Hillary the statement is executed as long as the corresponding condition is met, and then exits if-else control flow and moves to return(ti)

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