R语言循环绘图生成空白PDF，单独运行循环内代码功能正常

核心触发原因 #

R环境中，交互式执行代码时会自动打印绘图函数返回的绘图对象、完成图形渲染；但在循环体内执行时不会触发自动打印逻辑，绘图结果无法写入打开的PDF设备，最终生成空白PDF文件，完全匹配「单步执行正常、循环执行空白」的特征。

修复方案 #

按以下规则修改代码即可：

• 所有绘图语句外层包裹print()强制渲染
• 循环执行前先创建输出目录，避免路径不存在导致写入失败
• 循环开头关闭残留的绘图设备，避免状态异常

修改后代码 #

# 提前创建输出目录
dir.create("results/out_of_sample", recursive = TRUE, showWarnings = FALSE)
# 关闭所有残留绘图设备
graphics.off()

for (garch_model_name in c('sGARCH', 'eGARCH', 'gjrGARCH')) {
  dist = 'jsu'
  p = 1
  q = 1

  print(garch_model_name)
  
  roll = list('start'=N, 'window'='expanding', 'k'=1) 
  res = fit_GARCH(ret_d, resample=list(period='days', k=1), garchModel=garch_model_name, garchOrder=c(q,p), distModel=dist, roll=roll)
  spec = res$model
  mod = res$fit
  
  df = mod@forecast$density
  xdf = as.xts(df)
  tzone(xdf) = 'UTC'
  predictions = xdf$Sigma
  
  predictions_list[[garch_model_name]] = predictions
  
  realized = tail(RV, M)
  
  rmse_list[[garch_model_name]] = calc_rmse(predictions, realized)
  mae_list[[garch_model_name]] = calc_mae(predictions, realized)
  rmedse_list[[garch_model_name]] = sqrt(median((realized - predictions)^2))
  mape_list[[garch_model_name]] = mean(abs((realized - predictions)/realized))
  
  mz = lm(realized ~ predictions)
  s = summary(mz)
  mz_list[[garch_model_name]] = s$r.squared
  
  df = cbind(realized, predictions)
  colnames(df) = c('Realized', 'Forecast')
  pdf(file=sprintf('results/out_of_sample/realized_predicted_%s.pdf', garch_model_name))
  # 新增print强制渲染
  print(plot.xts(df, main='Realized vs Forecast', legend.loc='topright', col=c('black', 'red'), lty=c(1,1), lwd=c(1,2)))
  dev.off()
  
  errors = (realized - predictions)/realized * 100
  
  pdf(file=sprintf('results/out_of_sample/forecast_errors_%s.pdf', garch_model_name))
  # 新增print强制渲染
  print(plot(errors, main=garch_model_name, ylab='% error'))
  dev.off()
}

内容的提问来源于stack exchange，提问作者s5s