从R包函数中检索并执行示例代码作为R-markdown中的代码块

Question

我想从R包中提取示例代码，并自动在rmarkdown文件中运行。

我能够使用函数utils::example提取代码，如下所示。

example("geom_histogram", package = "ggplot2", ask = F,
         prompt.prefix = "", give.lines = TRUE)[-(1:5)]

我尝试使用块选项results="asis"，如下所示，但结果是作为代码输出而不是代码块提供的。

```{r,echo = FALSE, results="asis"}
cat("```{r}")
library(ggplot2)
cat(paste(example("geom_histogram", package = "ggplot2", ask = F,
                  prompt.prefix = "", give.lines = TRUE)[-(1:5)], collapse = "\n"))
cat("```")
```

我希望将代码作为代码块，并将输出与http://ggplot2.tidyverse.org/reference/geom_histogram.html中的相同。怎么做到这一点？

Answer 1

更新回答：

您可以创建一个函数来提取代码并将其用作块选项中的code参数。

# Function saved in functions.R file
getCode <- function(myFunction, myPackage) {
    example(myFunction, myPackage, ask = FALSE, character.only = TRUE,
            prompt.prefix = "", give.lines = TRUE)[-(1:5)]
}

您的Rmd（myFile.Rmd）应如下所示：

```{r, meta, include = FALSE}
myPackage  <- "ggplot2"
myFunction <- "geom_histogram"
source("functions.R")
```

```{r, intro, echo = FALSE, results = "asis"}
cat("#", myPackage, "\n")
cat("##", myFunction, "\n")
library(myPackage, character.only = TRUE)
```

```{r, runCode, code = getCode(myFunction, myPackage)}
```

使用Rmd编织knitr::knit2html("myFile.Rmd")，得到如下结果：

上一个回答：

将提取的代码写入虚拟文件（foo.R）并将其用作块选项中的code参数。

示例文件（myFile.Rmd）：

• 第一个块：加载测试库
• 第二个块：提取示例并将其保存到文件
• 第三个块：运行解压缩的代码

```{r, meta, include = FALSE}
library(ggplot2)
```

```{r, getCode, include = FALSE}
code <- example("geom_histogram", package = "ggplot2", ask = FALSE,
                prompt.prefix = "", give.lines = TRUE)[-(1:5)]
write.table(code, "foo.R", quote = FALSE, row.names = FALSE, col.names = FALSE)
```

```{r, runCode, code = readLines("foo.R")}
```

使用knitr::knit2html("myFile.Rmd")编织文件，得到如下结果：

我们还可以删除硬编码变量以获得更灵活的输出：

```{r, meta, include = FALSE}
myPackage  <- "ggplot2"
myFunction <- "geom_histogram"
library(myPackage, character.only = TRUE)
```

```{r, getCode, include = FALSE}
code <- example(myFunction, myPackage, ask = FALSE, character.only = TRUE,
                prompt.prefix = "", give.lines = TRUE)[-(1:5)]
write.table(code, "foo.R", quote = FALSE, row.names = FALSE, col.names = FALSE)
```

```{r, intro, echo = FALSE, results = "asis"}
cat("#", myPackage, "\n")
cat("##", myFunction, "\n")
```

```{r, runCode, code = readLines("foo.R")}
```