如何在 foreach 循环中进行 clusterExport（操作系统：Windows）

Question

我有以下问题。我需要全局环境中变量的时间索引，但是当我想在全局环境的并行处理期间将它们导出到集群中时，我收到以下消息：

{ 中的错误：任务 1 失败 - “找不到对象‘Szenario’”

我的原始代码的一个最小示例，它会产生错误：

    Historical <- structure(c(18.5501872568473, 24.3295787432955, 14.9342384460288, 
    13.0653757599636, 8.67294618896797, 13.4587662721594, 20.792126254714, 
    17.5162747884424, 28.8253151239752, 23.0568765432192), index = structure(c(-7305, 
    -7304, -7303, -7302, -7301, -7300, -7299, -7298, -7297, -7296
    ), class = "Date"), class = "zoo")

    Szenario <- structure(c(10.2800684124652, 14.5495871489361, 9.8565852930294, 
    21.1654540678686, 21.1936990312861, 12.4209005842752, 9.77473132000267, 
    17.1997402736739, 17.884107611858, 13.622588360244), index = structure(c(13149, 
    13150, 13151, 13152, 13153, 13154, 13155, 13156, 13157, 13158
    ), class = "Date"), class = "zoo")

    library(doParallel)   
    library(foreach)     
    library(raster)
    library(zoo)
    library(parallel)

    # Parallelisation Settings
    # Definition of how many cores you want to use
    UseCores <- detectCores() -2 # -1 at max because one core has to be used for other tasks 
    # Register CoreCluster
    cl <- makeCluster(UseCores)
    registerDoParallel(cl)

foreach(fn=1:1) %dopar% {

  library(raster) # needed libraries have to be loaded inside the loop, while parallel processing occurs
  library(zoo)
  library(base)
  library(parallel)

  #In my original script, I'm looping through Filenames, which are called like my variables in my Global environment (without .tif at the end of the filename), variables names are saved as characters
  file.referenz.name <- c("Historical")
  file.szenario.name <- c("Szenario")

  #Create timeindex für rasterstacks to subset later on with them (getZ, setZ)

  clusterExport(cl, varlist = c(file.szenario.name, file.referenz.name), envir = .GlobalEnv)
  time.index.szenario <- index(get(file.szenario.name))
  time.index.referenz <- index(get(file.referenz.name))

}

#end cluster
stopCluster(cl)

Answer 1

试试这个

foreach(fn=1:1, .export=c("Szenario"), 
                .packages=c("raster", "zoo", "base", "parallel") %dopar%

在%dopar% {} 中的clusterExport 令人困惑。您可以在foreach 之前将clusterExport 到每个cl，或者在foreach 中简单地使用.export

您可以删除%dopar% {} 中的library 语句。