rmarkdown 中的 YAML 当前日期 [英] YAML current date in rmarkdown

问题描述

我想知道是否有一个技巧可以将当前日期放在 .rmd 文档的 YAML 前端，以由 knitr 和 处理>rmarkdown 包.我曾经在我的 wiki 页面顶部有以下行，

I'm wondering if there's a trick to put the current date in the YAML front-matter of a .rmd document to be processed by knitr and the rmarkdown package. I used to have the following line at the top of my wiki pages,

   _baptiste, `r format(Sys.time(), "%d %B, %Y")`_

它会在 html 输出中转换为 baptiste, 03 May, 2014.现在，我想利用 rmarkdown 提供的高级 pandoc 包装器，但是在 YAML 标头中包含 r 代码似乎不起作用:

and it would get converted to baptiste, 03 May, 2014 in the html output. Now, I would like to take advantage of the advanced pandoc wrapper provided by rmarkdown, but having r code in the YAML header doesn't seem to work:

---
title: "Sample Document"
output:
  html_document:
    toc: true
    theme: united
date: `r format(Sys.time(), "%d %B, %Y")`
author: baptiste
---

Error in yaml::yaml.load(front_matter) : 
  Scanner error: while scanning for the next token at line 6, column 7
 found character that cannot start any token at line 6, column 7
Calls: <Anonymous> ... output_format_from_yaml_front_matter -> 
       parse_yaml_front_matter -> <Anonymous> -> .Call

有什么解决方法吗?

推荐答案

这有点棘手，但您只需通过引用内联 R 表达式使 date 字段在 YAML 中有效，例如

This is a little bit tricky, but you just need to make the date field valid in YAML by quoting the inline R expression, e.g.

date: "`r format(Sys.time(), '%d %B, %Y')`"

然后解析错误将消失，并且日期将在markdown输出中生成，因此Pandoc可以使用来自Sys.time()的值.

Then the parsing error will be gone, and the date will be generated in the markdown output so Pandoc can use the value from Sys.time().

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