禁止(或隐藏)R中自定义函数的特定返回值 [英] Suppress(or hide) the specific return value of customized function in R

问题描述

有一个简单的R功能代码.

There is a simple R function code.

fx <- function(x){

  lst <- list(a = x+1, b = x*2, c = x+c(1:100))
  return(lst)

}

在这段代码中，我想隐藏'lst $ c'元素，因为数据很长. 所以，我在下面尝试过

In this code, I want to hide 'lst$c' element because the data is long. So, I tried below

fx <- function(x){

 lst <- list(a = x+1, b = x*2, c = x+c(1:100))
 return(lst[c(1,2)])

}

object <- fx(1)
object

并获得

###
$a
[1]2

$b
[1]2

和

fx <- function(x){

 lst <- list(a = x+1, b = x*2, c = x+c(1:100))
 invisible(lst)

}

object <- fx(1)
object

###
$a
[1]2

$b
[1]2

$c
[1]2 3 4 5 ....101

但是当我将此函数分配给对象时，我不想丢失"lst $ c"数据 像这样.

but I don't wanna lose the 'lst$c' data when I assign this function to object like this.

object <- fx(2)
object

## No return 'lst$c'.
$a
[1]2

$b
[1]2

str(object)

## not include 'lst$c'
List of 2
$ a: num 2
$ b: num 2

所以，我想要...

object

###
$a
[1]2

$b
[1]2

str(object)

## still have lst$c data in the data structure
List of 3
$ a: num 2
$ b: num 2
$ c: num [1:100] 2 3 4 5 6 7 ...

我该怎么做?

推荐答案

由@nrussell实现注释.你可以做这样的事情

To implement comments by @nrussell. You can do something like this

fx <- function(x){    
    lst <- list(a = x+1, b = x*2, c = x+c(1:100))
    class(lst) <- "foo"  # assign the class attribute to your returning result
    return(lst)     
}

print.foo <- function(x) print(x[c(1,2)])  # define a new print function for the foo class

fx(3)        # now it prints only the first two elements
# $a
# [1] 4

# $b
# [1] 6

str(fx(3))   
# List of 3
#  $ a: num 4
#  $ b: num 6
#  $ c: num [1:100] 4 5 6 7 8 9 10 11 12 13 ...
#  - attr(*, "class")= chr "foo"

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