Knitr:Markdown文档中LaTeX环境中的R代码 [英] Knitr: R code within LaTeX environment in a Markdown document

问题描述

我在Markdown中有一个文档，该文档通过Knitr并入了R代码.为了渲染方程式，我使用LaTeX，只需在文本中编写其命令即可.假设我有以下LaTeX代码:

I have a document in Markdown, which incorporates R code via Knitr. For rendering equations I use LaTeX, simply writing its commands in the text. Say I have the following LaTeX code:

\begin{displaymath}
\mathbf{X} = \begin{bmatrix}
2 & 12\\ 
3 & 17\\ 
5 & 10\\ 
7 & 18\\ 
9 & 13\\
\end{bmatrix}
\end{displaymath}

当我将所有内容转换为PDF时，这为我提供了一个很好的数学矩阵表示形式(完整的工作流程为:RMD-> knitr-> MD-> pandoc-> TeX-> pandoc-> PDF) .

Which renders me a nice mathematical matrix representation (in square brackets), when I convert everything to PDF (the full workflow is then: RMD -> knitr -> MD -> pandoc -> TeX -> pandoc -> PDF).

现在，假设我们希望从R对象(某些R矩阵x)即时生成所述矩阵.在这篇文章，我们确定了如何生成所需的LaTeX代码(在此处定义了matrix2latex()函数).现在的问题是如何获取Knitr对其进行评估.我尝试了以下代码:

Now, suppose we want the said matrix to be generated on-the-fly from an R object, some R matrix x. In this post we establish how to generate the required LaTeX code (the matrix2latex() function is defined there). The question now is how to get Knitr to evaluate it. I tried the following code:

\begin{displaymath}
\mathbf{X} = `r matrix2latex(x)`
\end{displaymath} 

，但是它只是在R输出应该产生的地方产生空白(实际上为NULL).令我感到惊讶的是，这还没有被问到(至少我自己的搜索没有产生任何结果).任何想法如何使这项工作?

but it simply produces blank space (NULL actually) where the R output should be. I am surprised this hasn't been asked already (at least my own search yielded nothing). Any ideas how to make this work?

如建议的那样，重写不带cat()的功能.这是该函数的工作版本，以供将来参考:

As suggested, rewrote the function without cat(). Here is the working version of the function for future reference:

m2l <- function(matr) {

    printmrow <- function(x) {

        ret <- paste(paste(x,collapse = " & "),"\\\\")
        sprintf(ret)
    }

    out <- apply(matr,1,printmrow)
    out2 <- paste("\\begin{bmatrix}",paste(out,collapse=' '),"\\end{bmatrix}")
    return(out2)
}

推荐答案

这是因为您的matrix2latex函数使用cat并将其输出发送到标准输出流，而knitr却不在此位置放输出.

This is because your matrix2latex function uses cat and sends its output to the standard output stream, which isn't where knitr is trying to put the output.

两种解决方案:一种是重写您的函数，以使用paste和sprintf或其他字符串格式函数将输出构造为字符串，或者作为一种快速破解方法，只需将其包装在capture.output中:

Two solutions: one is to rewrite your function to construct the output as a string using paste and sprintf or other string formatting functions, or as a quick hack just wrap it in capture.output thus:

m2l = function(matr){capture.output(matrix2latex(matr))}

然后在您的.Rmd文件中:

\begin{displaymath}
\mathbf{X} = `r m2l(x)`
\end{displaymath}

成为

\mathbf{X} = \begin{bmatrix} , 0.06099 & 0.768 \\ , 0.6112 & 0.004696 \\ , 0.02729 & 0.6198 \\ , 0.8498 & 0.3308 \\ , 0.6869 & 0.103 \\ , \end{bmatrix}

虽然不是很完美，但确实说明了原理.内联表达式插入的代码是它的值，而不是它打印或显示的内容.

which although isn't quite perfect does illustrate the principle. The code inserted by the inline expression is the value of it, not what it prints or cats.

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