如何在R的fable包中按分组批量生成单独预测图并保存？

问题场景 #

使用R的fable包完成都市区预测后，希望为64个都市区单独生成预测图（而非用facet_wrap合并展示），但执行以下代码时出现错误：

forecastplots <- forecasts %>% group_by(Metro) %>% autoplot(fabledata) 

错误信息

Error in `hilo()`:
! Objects of type `grouped_ts` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
• Objects of type `grouped_df` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
• Objects of type `tbl_ts` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
• Objects of type `tbl_df` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
• Objects of type `tbl` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
• Objects of type `data.frame` are not supported by `hilo()`, you can create a custom `hilo` with `new_hilo()`
Run `rlang::last_error()` to see where the error occurred.

错误核心：group_by()生成的分组对象（grouped_ts）无法被autoplot.fable依赖的hilo()函数处理，必须将每个都市区的预测数据单独拆分后再绘图。

解决方案：批量生成并保存到PDF #

无需逐个手动筛选都市区，用dplyr+purrr的组合即可实现自动化批量处理，以下提供两种可行方法：

方法1：用group_split拆分后遍历绘图

library(fable)
library(tsibble)
library(dplyr)
library(purrr)
library(ggplot2)

# 1. 按Metro字段拆分预测数据，得到每个都市区的独立数据集
metro_forecast_list <- forecasts %>% 
  group_split(Metro, .keep = TRUE)

# 2. 遍历生成每个都市区的预测图，自动添加标题
metro_plot_list <- metro_forecast_list %>% 
  map(function(metro_data) {
    autoplot(metro_data, fabledata) +
      labs(title = unique(metro_data$Metro),
           x = "时间", y = "预测值") +
      theme_minimal()
  })

# 3. 将所有图批量保存到单个PDF文件
pdf("所有都市区预测图.pdf", width = 10, height = 6)
walk(metro_plot_list, print)  # 逐个打印绘图对象到PDF
dev.off()

方法2：用nest嵌套数据后生成图列

library(fable)
library(tsibble)
library(dplyr)
library(purrr)
library(ggplot2)

# 1. 按Metro嵌套数据，生成包含每个都市区预测数据的列表列
nested_forecasts <- forecasts %>%
  nest(forecast_data = -Metro)

# 2. 生成每个都市区的预测图，存储到新的plot列
nested_forecasts <- nested_forecasts %>%
  mutate(plot = map2(forecast_data, Metro, ~{
    autoplot(.x, fabledata) +
      labs(title = .y, x = "时间", y = "预测值") +
      theme_minimal()
  }))

# 3. 提取所有图并保存到PDF
pdf("所有都市区预测图.pdf", width = 10, height = 6)
walk(nested_forecasts$plot, print)
dev.off()

内容的提问来源于stack exchange，提问作者John Meszaros