Updating variable value after redefinition

Question

A newbie question for you R folks:

Case scenario:

1. I define variable A: A=number

2. I define other variables based on A: B=number*A

3. I change the definition of A: A=different number

[Q]. How can I get R to automatically update the value of B, without redefining it again?

E.g.: 1. A=1000; 2. B=A/10; (B=100) 3. Changed my mind: A=1100 after all;

>A
1100
>B
100

B should be 110 (1100/10), but its value has not been updated - hence it reads 100. Without redefining B, how can I update its value?

Thanks!

Answer 1

Try this:

A <- 1000
makeActiveBinding("B", function() A/10, .GlobalEnv)
B
## [1] 100
A <- 1100
B
## [1] 110

Answer 2

You are proposing making B a function of A (and possibly of the "number" in that second expression)

A=10
B <- function(Number=3.5) { A*Number }
B()
# [1] 35
A <- 15
B()
# [1] 52.5