Knitr文档中的install.packages失败: [英] install.packages fails in knitr document: "trying to use CRAN without setting a mirror"

问题描述

使用以下代码，我获得了所需的数据，但是由于某些原因，我无法弄清knitr并不允许我编译PDF文档，如下所示:

Using the following code I got the data I wanted, but for some reason I can't figure out knitr doesn't let me compile a PDF document, as shown further below:

我的代码:

install.packages("weatherData")
library(weatherData)
istanbul <- getWeatherForDate("Istanbul",
                              start_date = Sys.Date() - 41, 
                              end_date = Sys.Date())

正常工作，但尝试编译PDF时收到以下消息:

Works out with no problem but I get the following message trying compile the PDF:

Quitting from lines 3-31 (ist_weather.spin.Rmd) 
Error in contrib.url(repos, type) : 
  trying to use CRAN without setting a mirror
Calls: <Anonymous> ... eval -> eval -> install.packages -> grep -> contrib.url
Execution halted

推荐答案

除非您特别要求，否则Knitr会产生一个R会话，而没有默认的cran镜像.我们往往会忘记使用Rstudio时需要为每个R会话设置CRAN，因为它会处理它，但仅用于交互用途，而不用于knitr.

Knitr produces a R session, without a default cran mirror unless you specifically asked for one. We tend to forget we need to set up CRAN for every R session when we use Rstudio because it takes care of it, but only for interactive use, not for knitr.

您可以尝试将镜像指定为install.packages参数:

You could try specifying a mirror as a install.packages argument:

install.packages("weatherData",repos = "http://cran.us.r-project.org")

或者，您可以在.Rprofile中设置默认的CRAN镜像.参见此答案.

Alternatively, you could set up your default CRAN mirror in your .Rprofile. See this answer.

也就是说，通过可能会多次编译的knitr文档安装软件包并不是一个好主意.您应该假设人们知道如何在需要时安装丢失的软件包，或者至少在再次安装之前测试该软件包是否已安装

That said, it is not a good idea to install packages through a knitr document that you will probably compile several times. You should assume people know how to install a missing package if needed, or at least test whether the package is installed before installing it again

if(!require(weatherData)) install.packages("weatherData",repos = "http://cran.us.r-project.org")

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