mixed-programming.Rmd

# 混合编程 {#chap-mixed-programming}

```{r,include=FALSE}
library(magrittr)
library(shiny)
library(htmlwidgets)
library(reticulate)
library(Rcpp)
knitr::opts_chunk$set(python.reticulate = TRUE)
reticulate::use_virtualenv(virtualenv = Sys.getenv("RETICULATE_PYTHON_ENV"), required = TRUE)
```

R 语言 [@Ross_1996_R] 是一个统计计算和绘图的环境，以下各个节不介绍具体 R 包函数用法和参数设置，重点在历史发展趋势脉络，详细介绍去见[《现代统计图形》](https://bookdown.org/xiangyun/msg)的相应章节。R 语言的目标在于统计计算和绘图，设计优势在数据结构、图形语法、动态文档和交互图形

<!-- 介绍 R 与其它语言的异同，降低编程门槛 -->


## 函数源码 {#sec-function-source}


[flow](https://github.com/moodymudskipper/flow) 包可以将函数调用的过程以流程图的方式呈现，代码结构一目了然，快速理清源代码

```{r,eval=FALSE}
remotes::install_github('moodymudskipper/funflow')
funflow::view_flow('median.default')
```

```{r}
methods(predict)
```

stats 包里找不到这个函数

```{r}
ls("package:stats", all.names = TRUE, pattern = "predict.poly")
```


```{r,error=TRUE}
predict.poly
```

可见函数 `predict.poly()` 默认没有导出

```{r}
stats:::predict.poly
```

或者

```{r}
getAnywhere(predict.poly)
```

```{r}
getAnywhere("predict.poly")$where
```

函数参数个数

```{r}
names(formals(read.table))
```


## 命名约定 {#sec-naming-conventions}

R 语言当前的命名状态  <https://journal.r-project.org/archive/2012-2/RJournal_2012-2_Baaaath.pdf> 和 <https://essentials.togaware.com/StyleO.pdf>


R 与不同的编程语言如何交互

## R 与 JavaScripts {#sec-r-javascripts}

<!-- roughviz.js 为例介绍如何使用 htmlwidgets 制作将 JavaScripts 库打包成 R 包 -->

```{r}
library(htmlwidgets)
```

## R 与 Python {#sec-r-python}

R 包 knitr 和 reticulate 支持 R Markdown 文档中嵌入 Python 代码块， reticulate 包还支持 Python 和 R 之间的数据对象通信交流。

```{r}
library(reticulate)
```

如图 \@ref(fig:reticulate-matplotlib) 所示，在 R Markdown 中执行 Python 绘图代码，并且将图形插入文档。

```{python reticulate-matplotlib,fig.cap="Python 图形",collapse=TRUE, dev = ifelse(knitr::is_html_output(), 'svg', ifelse(knitr::is_latex_output(), 'pdf', 'png')), out.width='.8\\textwidth'}
import matplotlib.pyplot as plt
plt.switch_backend('agg')

plt.plot([0, 2, 1, 4])
plt.show()
```


## R 与 C {#sec-r-c}

knitr 支持在 R Markdown 中嵌入 C 语言代码

```{c}
void useC(int *i){
  i[0] = 11;
}
```
```{r}
a <- rep(2,10)
out <- .C("useC", b = as.integer(a))
out
out$b
```


一步一步地命令行操作

```bash
R CMD SHLIB useC1.c
```

```r
dyn.load("useC1.dll")
a <- rep(2,10)
out <- .C("useC", b = as.integer(a))
out$b
```


## R 与 C++ {#sec-r-cpp}

[Dirk Eddelbuettel](https://dirk.eddelbuettel.com) 是 Rcpp 的核心开发者。

- Dirk Eddelbuettel celebRtion 2020, Copenhagen, Denmark [Introduction to Rcpp: from simple examples to machine learning](https://dirk.eddelbuettel.com/papers/celebRtion_feb2020_rcpp.pdf)
- Online Tutorial for useR! 2020 [Seamless R and C++ Introduction with Rcpp](https://dirk.eddelbuettel.com/papers/useR2020_rcpp_tutorial.pdf) 视频 https://vimeo.com/438283959
- James Balamuta [unofficial rcpp api documentation](https://thecoatlessprofessor.com/programming/unofficial-rcpp-api-documentation/) <https://github.com/coatless/rcpp-api>
- Rcpp for everyone <https://github.com/teuder/rcpp4everyone_en>
- 课程 [Foundations of Data Science](https://ds4ps.org/cpp-526-sum-2020/)

```{r}
library(Rcpp)
```

## R 与 LaTeX {#sec-r-latex}

<!-- TeX 的历史一小段介绍，tikzDevice 对公式的加强， 引入 TikZ 图形，常用 LaTeX 语法 <https://wch.github.io/latexsheet/latexsheet-a4.pdf> -->

**tikzDevice** 包将 LaTeX 公式和绘图系统 [TikZ](https://en.wikipedia.org/wiki/PGF/TikZ) 引入 R 语言生态，贡献在于提供更加漂亮的公式输出，对图形进行后期布局排版加工，达到设计师出品的质量水平。图 \@ref(fig:tex-system) 展示了复杂的 TeX 生态系统， R 语言只是取其精华，使用 TikZ 绘制。

```{r tex-system, engine="tikz", fig.cap="TeX 系统", cache=TRUE, engine.opts=list(extra.preamble=c("\\usepackage[default]{sourcesanspro}","\\usetikzlibrary{mindmap}"))}
\begin{tikzpicture}
  \path [
    mindmap,
    text = white,
    level 1 concept/.append style =
      {font=\Large\bfseries\sffamily, sibling angle=90, level distance=125},
    level 2 concept/.append style =
      {font=\normalsize\bfseries\sffamily},
    level 3 concept/.append style =
      {font=\small\bfseries\sffamily},
    tex/.style     = {concept, ball color=blue,
      font=\Huge\bfseries},
    engines/.style = {concept, ball color=green!50!black},
    formats/.style = {concept, ball color=purple!50!black},
    systems/.style = {concept, ball color=red!90!black},
    editors/.style = {concept, ball color=orange!90!black}
  ]
  node [tex] {\TeX} [clockwise from=0]
    child[concept color=green!50!black, nodes={engines}] {
      node {Engines} [clockwise from=90]
        child { node {\TeX} }
        child { node {pdf\TeX} }
        child { node {XeTeX} }
        child { node {Lua\TeX} }}
    child [concept color=purple, nodes={formats}] {
      node {Formats} [clockwise from=300]
        child { node {\LaTeX} }
        child { node {Con\TeX t} }}
    child [concept color=red, nodes={systems}] {
      node {Systems} [clockwise from=210]
        child { node {\TeX Live} [clockwise from=300]
          child { node {Mac \TeX} }}
        child { node {MiK\TeX} [clockwise from=60]
          child { node {Pro \TeX t} }}}
    child [concept color=orange, nodes={editors}] {
      node {Editors} [clockwise from=180]
        child { node {WinEdt} }
        child { node {\TeX works} }
        child { node {\TeX studio} }
        child { node {\TeX maker} }};
\end{tikzpicture}
```


## 运行环境 {#sec-mixed-programming-session-info}

```{r}
sessionInfo()
```