r - 避免全局变量

Question

我想制作一个基本的分析工具来收集时间戳并生成带有注释的运行时间。唯一的问题是我无法弄清楚如何在不使用全局变量的情况下做到这一点。实现我想要实现的功能的“正确”方法是什么？如果 R 已经内置了这个功能，那就太棒了，但我在这里真正想弄清楚的是如何避免使用全局变量并编写更健壮的代码。

timeStamps = c()
runTimes = list()

appendRunTimes <- function(note) {
  if(length(timeStamps) < 1) {
    timeStamps <<- Sys.time()
  }
  else {
    timeStamps <<- c(timeStamps, Sys.time())
    diff <- timeStamps[length(timeStamps) ] - timeStamps[length(timeStamps) - 1]
    runTimes <<- c(runTimes,  format(diff))
    names(runTimes)[length(runTimes)] <<-  note
  }

}


appendRunTimes('start')
Sys.sleep(4)
appendRunTimes('test')

score 8 · Accepted Answer

这是您使用闭包重写的示例：

RTmonitor <- local({
  timeStamps = c()
  runTimes = list()

  list(
    appendRunTimes=function(note) {
      if(length(timeStamps) < 1) {
        timeStamps <<- Sys.time()
      }
      else {
        timeStamps <<- c(timeStamps, Sys.time())
        diff <- timeStamps[length(timeStamps) ] - timeStamps[length(timeStamps) - 1]
        runTimes <<- c(runTimes,  format(diff))
        names(runTimes)[length(runTimes)] <<-  note
      }
    },
    viewRunTimes=function() {
      return(list(timeStamps=timeStamps,runTimes=runTimes))
    })
})


> RTmonitor$appendRunTimes("start")
> RTmonitor$appendRunTimes("test")
> RTmonitor$viewRunTimes()
$timeStamps
[1] "2013-01-04 18:39:12 EST" "2013-01-04 18:39:21 EST"

$runTimes
$runTimes$test
[1] "8.855587 secs"

观察值存储在闭包内，而不是全局环境中：

> timeStamps
Error: object 'timeStamps' not found
> runTimes
Error: object 'runTimes' not found
> RTmonitor$timeStamps
NULL
> RTmonitor$runTimes
NULL

更多关于闭包和避免全局变量的阅读：

score 4 · Accepted Answer

现在使用 ReferenceClasses 来做到这一点：

RTmonitor = setRefClass("RTmonitor",
  fields=list(
    timeStamps="POSIXct",
    runTimes = "list"
    ),
  methods=list(
    appendRunTimes=function(note){
      if(length(timeStamps)==0){
        timeStamps <<- Sys.time()
      }else{
        timeStamps <<- c(timeStamps, Sys.time())
        diff <- timeStamps[length(timeStamps) ] - timeStamps[length(timeStamps) - 1]
        runTimes <<- c(runTimes,  format(diff))
        names(runTimes)[length(runTimes)] <<-  note
      }
    }
    )
  )

现在您已经定义了一个类，实例化一个对象并使用它：

> r = RTmonitor$new()
> r$appendRunTimes("start")
> r$appendRunTimes("test")
> r
Reference class object of class "RTmonitor"
Field "timeStamps":
[1] "2013-01-05 14:52:25 GMT" "2013-01-05 14:52:31 GMT"
Field "runTimes":
$test
[1] "5.175815 secs"

与闭包方法非常相似，但更正式。例如，我必须将timeStamps字段定义POSIXct为。您也可以通过RTmonitor这种方式创建多个对象并且它们独立工作——您必须编写一个封装了闭包的闭包构造函数才能做到这一点。

r - 避免全局变量

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