如何在r中转换函数的对象？

Question

I want to create a function that transforms its object.

I have tried to transform the variable as you would normally, but within the function.

This works:

vec <- c(1, 2, 3, 3)
vec <- (-1*vec)+1+max(vec, na.rm = T)
[1] 3 2 1 1

This doesn't work:

vec <- c(1, 2, 3, 3)

func <- function(x){
  x <- (-1*x)+1+max(x, na.rm = T))
}

func(vec)
vec
[1] 1 2 3 3

Answer 1

R is functional so normally one returns the output. If you want to change the value of the input variable to take on the output value then it is normally done by the caller , not within the function. Using func from the question it would normally be done like this:

vec <- func(vec)

Furthermore, while you can overwrite variables it is, in general, not a good idea. It makes debugging difficult. Is the current value of vec the input or output and if it is the output what is the value of the input? We don't know since we have overwritten it.

func_ovewrite

That said if you really want to do this despite the comments above then:

# works but not recommended
func_overwrite <- function(x) eval.parent(substitute({
  x <- (-1*x)+1+max(x, na.rm = TRUE)
}))


# test
v <- c(1, 2, 3, 3)
func_overwrite(v)
v
## [1] 3 2 1 1

Replacement functions

Despite R's functional nature it actually does provide one facility for overwriting although the function in the question is not really a good candidate for it so let us change the example to provide a function incr which increments the input variable by a given value. That is, it does this:

x <- x + b

We can write this in R as:

`incr<-` <- function(x, value) x + value

 # test
 xx <- 3
 incr(xx) <- 10
 xx
 ## [1] 13

T vs. TRUE

One other comment. Do not use T for true. Always write it out. TRUE is a reserved name in R but T is a valid variable name so it can lead to hard to find errors such as when someone uses T for temperature.