R Function using the result inside the function - r

Question

I have one variable A
0
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
which is an input into the following function
NoBeta <- function(A)
{
return(1-(1- B * (1-4000))/EXP(0.007*A)
}
The variable B is the result of this function how do I feed the result back into the function to calculate my next result?
Here is B
0
0.07
0.10
0.13
0.16
0.19
0.22
0.24
0.27
0.30
0.32
0.34
0.37
0.39
0.41
0.43
0.45
0.47
So the function needs to return the values of B but also using B e.g. if we using A 10 as input then the input for B is 0, when the input for A is 15 the input for B is the result from the previous calculation 0.07
B is calculated with the following formula in Excel
=1-(1-B1*(1-4000))/EXP(0.007*$A2)
How do I implement this formula in R?

Answer 1

If I understand your question correctly you wish to reference a previous row in a calculation for the current row.
You can adapt a function that was provided in another SO question here.
rowShift <- function(x, shiftLen = 1L) {
r <- (1L + shiftLen):(length(x) + shiftLen)
r[r<1] <- NA
return(x[r])
}
test <- data.frame(x = c(1:10), y = c(2:11))
test$z <- rowShift(test$x, -1) + rowShift(test$y, -1)
> test
x y z
1 1 2 NA
2 2 3 3
3 3 4 5
4 4 5 7
5 5 6 9
6 6 7 11
7 7 8 13
8 8 9 15
9 9 10 17
10 10 11 19
Then what you want to achieve becomes
test$z2 <- 1- (1-rowShift(test$x, -1)*(1-4000))/exp(0.007*rowShift(test$y, -1))
> head(test)
x y z z2
1 1 2 NA NA
2 2 3 3 -3943.390
3 3 4 5 -7831.772
4 4 5 7 -11665.716
5 5 6 9 -15445.790
6 6 7 11 -19172.560