R函数技术疑问：return语句内的表达式为何无法求值？

Hey there! Let's break down what's going wrong with your function and how to fix it quickly.

First, let's look at your original code:

f=function(x){return(list(y=x, z = y))}; f(1)

The Root Cause #

When you run this, you'll get an error saying Error in list(y = x, z = y) : object 'y' not found. Here's why:
In R, when you define the list inside return(), the y you're trying to use for z = y doesn't exist in the function's working environment yet. The y=x part is just defining a named element of the list, not creating a variable y that you can reference elsewhere in the same list definition. R looks for a variable named y in the current scope (the function's environment) and can't find it—hence the error.

Easy Fixes #

You have a couple of straightforward ways to fix this:

• Create the y variable first
  Define y as a separate variable in the function before building the list. This makes y available to use when setting z:

  f=function(x){
    y <- x
    return(list(y=y, z=y))
  }
  f(1)
  

• Reuse the original x directly
  If y is just a direct copy of x, you can skip creating a separate variable and just use x for both list elements:

  f=function(x){return(list(y=x, z=x))}
  f(1)
  

Either of these will return the expected output:

$y
[1] 1

$z
[1] 1

内容的提问来源于stack exchange，提问作者kevin