用 ggvis 将 RMarkdown 编织到 Word

当我尝试用以下内容编写 RMarkdown 文档时ggvis绘图到 Word，我从 Rstudio 收到以下消息。

Error: Functions that produce HTML output found in document targeting docx output.
Please change the output type of this document to HTML.
Execution halted

是否存在一个优雅的解决方案（无需太多努力）来实现这一点，也许使用export_png and vg2png?

这是一个例子：

```{r setup, include=FALSE}
library(dplyr)
library(ggvis)
```

The following table looks fine...
As long as I don't include this plot below

```{r, echo=FALSE, include=FALSE}
p <- pressure %>%
  ggvis(x = ~temperature, y = ~pressure) %>%
  layer_bars()
export_png(p, file = "hoge.png")
```

![](hoge.png)

如果你经常使用这个，你可以定义hook。