英文:
Recursive functions in R: How do I save the output of every call to a vector?
问题
如何保存每次调用vector函数的输出结果？我已经看到类似的问题，但要么表述不清晰，要么涉及更复杂的问题。对我以及其他初学者来说，看到最基本情况的解决方案将会很有帮助。
例如：
recursive = function(x) {
if (x < 1) {
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
[1] 0.1
[1] 0.2
[1] 0.3
[1] 0.4
[1] 0.5
[1] 0.6
[1] 0.7
[1] 0.8
[1] 0.9
[1] 1
[1] 1.1
这些输出如何直接编译成一个向量？
我尝试将它们追加到一个空向量中，但R不支持这种方法。
output <- c()
recursive = function(x) {
if (x < 1) {
output <- append(output, x + 0.1)
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
希望能提供一些帮助！
英文:
How can I save the output from each call to vector?
I have seen similar questions, but either poorly formulated or for more complicated problems. It would be helpful to me, and I am sure to other beginners, to see a solution for the most basic case.
For instance:
recursive = function(x) {
if (x < 1) {
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
[1] 0.1
[1] 0.2
[1] 0.3
[1] 0.4
[1] 0.5
[1] 0.6
[1] 0.7
[1] 0.8
[1] 0.9
[1] 1
[1] 1.1
How can these outputs be directly compiled to a vector?
I tried appending to an empty vector, but R disapproved of this approach.
output <- c()
recursive = function(x) {
if (x < 1) {
output <- append(output, x + 0.1)
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
Any help would be much appreciated!
答案1
得分: 2
你可以使用 _super assignment_ 中的 <<-。请参阅 帮助页面，以及更详细的信息，请查看《Advanced R》的 7.2.4 节。
基本上，函数内部创建/修改的变量不会传递到主环境。要实现这一点，你需要使用 <<-。
output <<- c()
recursive = function(x) {
if (x < 1) {
output <<- append(output, x + 0.1)
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
output
[1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
编辑： 正如Onyambu指出的，使用 <<- 是危险的，可能导致代码产生意外的副作用。我建议采纳他的建议！
英文:
You can use the super assignment <<-. See the the help page and, for more in depth info, the section 7.2.4 of "Advanced R".
Basically, variables created/modified inside a function don't go to the main environment. To achieve that, you need <<-.
output <- c()
recursive = function(x) {
if (x < 1) {
output <<- append(output, x + 0.1)
print(x + 0.1)
return(recursive(x + 0.1))
}
}
recursive(0)
output
[1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Edit: As Onyambu pointed out, using <<- is dangerous and can lead to unwanted side effects to your code. I recommend going with his answer!
答案2
得分: 2
以下是您要翻译的内容：
您可以简单地连接输出。注意：在使用 <<- 时要小心。
recursive = function(x) {
if (x < 1) c(x, recursive(x + 0.1))
else x
}
recursive(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
如果您需要明确使用 return 函数，您不需要使用 else：
recursive1 <- function(x) {
if (x < 1) return(c(x, recursive1(x + 0.1)))
x
}
recursive1(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
另一种方法是更改条件：
recursive2 <- function(x) {
if (x > 1) return(x)
c(x, Recall(x + 0.1))
}
recursive2(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
英文:
You can simply concatenate the output. Note: Be careful on the use of <<-.
recursive = function(x) {
if (x < 1) c(x, recursive(x + 0.1))
else x
}
recursive(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
If you need to explicitly use the return function, you do not need to use else:
recursive1 <- function(x) {
if (x < 1) return(c(x, recursive1(x + 0.1)))
x
}
recursive1(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Another way is to change the condition:
recursive2 <- function(x) {
if (x > 1) return(x)
c(x, Recall(x + 0.1))
}
recursive2(0)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
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