在R中缓存Vector的平均值(列表) [英] Caching the mean of a Vector in R (list)

问题描述

这是对

This is a follow up to Caching the mean of a Vector in R and is specifically about the last line of code

list(set = set, get = get, setmean = setmean, getmean = getmean)

我不了解list在做什么.在链接的问题上给出的答案:

I am not understanding what the list is doing. The answer given at the linked question:

list()返回包含所有已定义函数的特殊向量"

list() returns the 'special vector' containing all of the functions just defined

对我来说没有多大意义.我认为makeVector应该返回一个具有适当的set和get方法的对象，但是现在确定此list()的工作方式.左侧的set是什么，右侧的set是什么?

does not make much sense to me. I think that makeVector should be returning an object which has the approriate set and get methods, but now sure how this list() is doing that. What is the set on the left-hand side and what is the set on the right-hand side?

 makeVector <- function(x = numeric()) {
         m <- NULL
         set <- function(y) {
                x <<- y
                m <<- NULL
        }
        get <- function() x
        setmean <- function(mean) m <<- mean
        getmean <- function() m
        list(set = set, get = get,
             setmean = setmean,
             getmean = getmean)
 }

推荐答案

> z<- makeVector()
> z

上面的语句将返回"makeVector"函数中所有四个函数的列表，即$ set，$ get，$ setmean，$ getmean

$set
function (y) 
{
    x <<- y
    m <<- NULL
}
<environment: 0x0000000008935dc8>

$get
function () 
x
<environment: 0x0000000008935dc8>

$setmean
function (mean) 
m <<- mean
<environment: 0x0000000008935dc8>

$getmean
function () 
m
<environment: 0x0000000008935dc8>

现在您可以将每个函数作为列表对象进行访问，如下所示:

> z$set(c(1:20))
> z$get()
[1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> z$setmean(mean(z$get()))
> z$getmean()
[1] 10.5

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