r-打印循环内部的DiagrammeR对象

Question

有没有一种直接的方法可以在R Markdown文档的循环中打印DiagrammeR对象？我有一个文档，其中为多个模型分别生成了回归表、绘图和图表，并打印在一起。使用for循环很容易做到这一点，但DiagrammeR对象不会在循环中打印(即使使用像print(graph).这样的显式调用

其他地方对此进行了记录(参见：https://github.com/rich-iannone/DiagrammeR/issues/39(，但2015年提出的解决方案现在似乎不起作用(仅限于html输出(。

请参阅下面的Rmd示例代码。

---
title: "DiagrammeR loop test"
author: ""
date: "11/20/2020"
output: pdf_document
---

# Some header
Printing a single flowchart works fine in knitr using the DiagrammeR package. 
```{r figure_1, out.width = "15%", echo = FALSE, fig.align = 'center', fig.cap = "Flowchart 1: This prints fine."}
DiagrammeR::grViz(" 
digraph test {
node [shape = circle] 
A; B
A -> B
}
")
```
Flowchart 2 which is inside a loop, however, does not print 

```{r figure_2, out.width = "15%", echo = FALSE, fig.align = 'center', fig.cap = "Flowchart 2: These two diagrams do not print even with an explicit print command."}
for (i in 1:2){

graph <- DiagrammeR::grViz(" 
digraph test {
node [shape = circle] 
A; B
A -> B
}
")
print(graph)  
}

Answer 1

以下是修复方法：

# Create an empty list to save the htmlwidgets
plot_list <- htmltools::tagList()
for (i in 1:2){

graph <- DiagrammeR::grViz(" 
digraph test {
node [shape = circle] 
A; B
A -> B
}
")
# Store the htmlwidget inside this list
plot_list[[i]] <- graph 
}
#Print this list
plot_list