设置 knitr 以输出单独的图像

Question

我正在尝试将来自 knitr 输出的 PNG 图作为单独的文件写入磁盘，而无需手动执行。

我尝试了什么

• http://gforge.se/2014/01/fast-track-publishing-using-knitr-part-iii/ 中的 dev = 'png' 设置（this question 中也提到过）
• self_contained: no 来自knitr: include figures in report *and* output figures to separate files。

都没有用。运行编织过程的文件夹没有多余的文件，HTML 文档的源代码中嵌入了 base64 图像。

环境

• RStudio 0.99.903
• R 3.2.3
• knitr 1.15.1

MWE：RStudio RMarkdown 文件，添加了上述选项：

---
title: "Untitled"
output: html_document
self_contained: no
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
knitr::opts_chunk$set(dev="png", 
                      dev.args=list(type="cairo"),
                      dpi=96)
```

## R Markdown

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r cars}
summary(cars)
```

## Including Plots

You can also embed plots, for example:

```{r pressure, echo=FALSE}
plot(pressure)
```

Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.

Answer 1

self_contained 是 html_document 的一个选项，而不是顶级 YAML 设置。下面的文档仅使用它。 PNG 是默认的图形类型，因此您无需指定。

---
title: "Untitled"
output: 
  html_document:
    self_contained: no
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## Including Plots

You can also embed plots, for example:

```{r pressure, echo=FALSE}
plot(pressure)
```