Parellize xgboost建模模拟

Question

我必须对模型进行多次仿真。我试图在不同的内核上运行不同的仿真，并将结果保存到全局环境中。我有下面的代码不起作用。例如，我必须运行xgboost 3次（使用所有相同的参数，仅需重新运行3次，而我想在不同的内核上运行这3个仿真，并将imp_df_i返回到全局环境。

cores=detectCores()
cl <- makeCluster(cores[1]-1) #not to overload your computer
registerDoParallel(cl)

finalMatrix <- foreach(i=1:3, .combine=cbind) %dopar% {
require(xgboost)

  xgb_1 = xgboost(dtrain,
                  params = xgb_params_1,
                  nrounds = 3,                                                 # max number of trees to build
                  verbose = TRUE,                                         
                  print_every_n = 1,
                  early_stop_round = 10)                                          # stop if no improvement within 10 trees

  col_names = attr(tr.x, ".Dimnames")[[2]]
  imp = xgb.importance(col_names, xgb_1)               
  imp_df=data.frame(imp)
  assign(paste("imp_df",i, sep = "_"),imp_df,envir = .GlobalEnv )

  }
#stop cluster
stopCluster(cl)