r - 对于 R Markdown，如何从 R 变量显示矩阵

Question

我有一个 rmd 文档，其中包含以下内容

```{r code_block, echo=FALSE}
A = matrix(c(1,3,0,1),2,2)
B = matrix(c(5,3,1,4),2,2)
```

$$
\begin{bmatrix} 
1  & 0 \\ 
3 & 1 \\ 
\end{bmatrix}
*
\begin{bmatrix} 
5 & 1 \\ 
3 & 4 \\ 
\end{bmatrix}
$$

现在我想代替手动硬编码 LaTeX 部分，我可以使用变量 A 和 B 中的矩阵。这怎么可能？

谢谢。

Answer 1

这是 knitr::knit_print() 的完美用例.
您将找到有关 knitr::knit_print() 的详细信息其专用小插图中的方法:

vignette('knit_print', package = 'knitr')

目标是提供一个 knit_print类对象的方法 matrix .正如其他答案所建议的那样，定义运算符可能很有用。

您会在下面找到 Rmd为您的问题提供解决方案的文件。它还包含对运营商的建议。

这个答案的主要特点是你只需要写

`r A`

以 LaTeX 内联模式输出矩阵 A(没有 $ 输入)并写入

```{r echo=FALSE}
A
```

以 LaTeX 显示模式写入。

我还建议你定义一个 %times%运算符(operator)。因此，您只需编写:

`r A %times% B`

这个答案非常通用，您应该能够将其扩展到其他对象。

---
title: "R Markdown: Display a Matrix for R Variable"
author: "Romain Lesur"
output: 
  html_document:
    keep_md: true
---

```{r setup, include=FALSE}
# Define a generic method that transforms an object x in a LaTeX string
as_latex = function(x, ...) {
  UseMethod('as_latex', x)
}

# Define a class latex for LaTeX expressions
as_latex.character = function(x) {
  structure(
    paste(x, collapse = ' '), 
    class = c('latex', 'character')
  )
}

# A character string of class latex is rendered in display mode
# Define a knit_print() method for the latex class
knit_print.latex = function(x, ...) {
  knitr::asis_output(
    paste0('$$', x, '$$')
  )
} 

# Now, define a method as_latex for matrix
as_latex.matrix = function(x, ...) {
  as_latex(c(
    '\\begin{bmatrix}',
    paste(
      t(x),
      rep(c(rep('&', nrow(x) - 1), '\\\\'), ncol(x)),
      collapse = ''
    ),
    '\\end{bmatrix}'
  ))
}

# Indicate to knitr that matrix are rendered as latex
knit_print.matrix = function(x, ...) {
  knitr::knit_print(as_latex(x))
}

# Build a knitr inline hook to display inline latex in inline mode
default_inline_hook = knitr::knit_hooks$get('inline')
knitr::knit_hooks$set(inline = function(x) {
  x = paste(gsub('\\$\\$', '$', x))
  default_inline_hook(x)
})
```


```{r}
A = matrix(c(1,3,0,1),2,2)
B = matrix(c(5,3,1,4),2,2)
```


Now, matrix are rendered as LaTeX:

Matrix A in inline mode: `r A`

Matrix A in display mode:

```{r echo=FALSE}
A
```


### Operators

As other answers suggested, it could be useful to define operators.  
With the previous class, it is relatively straightforward:

```{r operators, include=FALSE}
`%times%` = function(x, y) {
  as_latex(sapply(list(x, '\\times', y), as_latex))  
}

`%add%` = function(x, y) {
  as_latex(sapply(list(x, '+', y), as_latex))  
}
```

Example in inline mode: `r A %add% A %times% B`

Display mode:
```{r echo=FALSE}
A %times% B
```