如何强制Knitr在所有其他代码块之后评估\ Sexpr

问题描述

我正在尝试为动态文档编写摘要，但是我的\Sexpr{}调用无法正常工作.

I am trying to write an abstract for a dynamic document, but my \Sexpr{} calls are not working.

基本上，我要做的就是从一个具有\Sexpr{value}生成的p值的摘要开始文档，其中的值被确定为文档中的下游".例如

Essentially all I am trying to do is start the document off with an abstract that has p-values generated from \Sexpr{value} where value is determined "downstream" in the document. For example

这有效:

\begin{document}

<<foo>>=
   value = 10
@

Today I bought \Sexpr{value} Salamanders

\end{document}

这不起作用(以及我要完成的工作)

This does not work (and what I am trying to accomplish)

\begin{document}

Today I bought \Sexpr{value} Salamanders

<<foo>>=
  value = 10
@

推荐答案

我没有看到直接的解决方案来在评估代码块之后推迟对\Sexpr的评估，但是将\Sexp与值结合使用仍然很容易例如，稍后在摘要中定义:使用单独的文件(myabstract.Rnw)作为摘要，在应该包含摘要的位置添加\input{myabstract}，并在主文档的最后添加knit myabstract.Rnw :

I don't see a straightforward solution to postpone evaluation of \Sexpr after evaluation of code chunks, but it is still easy to use \Sexp with values defined later in, for example, an abstract: Use a separate file (myabstract.Rnw) for the abstract, add \input{myabstract} where the abstract is supposed to be included and knit myabstract.Rnw at the very end of the main document:

document.Rnw:

document.Rnw:

\documentclass{article}
\begin{document}

\begin{abstract}
  \input{myabstract}
\end{abstract}

Main text.

<<>>=
answer <- 42
@

\end{document}

<<include = FALSE>>=
knit("myabstract.Rnw")
@

myabstract.Rnw:

myabstract.Rnw:

The answer is \Sexpr{answer}.

了解其工作原理的关键是要认识到knitr在LaTeX之前先处理文档.因此，LaTeX命令\input{myabstract}包含myabstract.tex"before"(不是指时间，而是指行号)并不重要，knit("myabstract.Rnw")会生成myabstract.tex.

Key to understanding how this works is to realize that knitr processes the document before LaTeX does. Therefore, it doesn't matter that the LaTeX command \input{myabstract} includes myabstract.tex "before" (not referring to time but referring to the line number), knit("myabstract.Rnw") generates myabstract.tex.

对于更复杂的场景，可以将评估和输出分开:在所有早期计算中进行所有计算，并将结果打印在其所属的位置.要显示源代码，请重用块(设置eval = FALSE).使用上面的示例，这意味着:

For more complex scenarios, evaluation and output could be separated: Do all the calculations in early chunks and print the results where they belong. To show source code, reuse chunks (setting eval = FALSE). Using the example from above, that means:

\documentclass{article}
\begin{document}

<<calculation, include = FALSE>>=
answer <- 42
@

\begin{abstract}
  The answer is \Sexpr{answer}.
\end{abstract}

Main text.

<<calculation, eval = FALSE>>=
@

\end{document}

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