如何判断某个软件包是否已安装? [英] How can I tell if a certain package was already installed?

问题描述

当我安装 yaml 包时，如果之前安装过 RStudio，则会在 RStudio 中弹出一条烦人的错误消息.如何判断软件包是否已安装，以便我可以在代码中决定是否安装软件包?

When I install the yaml package, an annoying error message pops up in RStudio if it had been previously installed. How can I tell if the package was already installed so I can decide in my code whether to install the package or not?

消息在一个弹出窗口中，它是:

The message is in a pop up window and it is:

此安装将更新的一个或多个软件包当前正在加载.在更新这些包之前重新启动 R 是强烈推荐.RStudio可以重新启动R然后自动重新启动后继续安装(所有工作和数据将被在重新启动期间保留).您想在此之前重新启动 R安装?

One or more of the packages that will be updated by this installation are currently loaded. Restarting R prior to updating these packages is strongly recommended. RStudio can restart R and then automatically continue the installation after restarting (all work and data will be preserved during the restart). Do you want to restart R prior to installing?

推荐答案

这将加载 yaml，如果尚未安装，请先安装:

This will load yaml, installing it first if its not already installed:

if (!require(yaml)) {
  install.packages("yaml")
  library(yaml)
}

或者如果你想参数化它:

or if you want to parameterize it:

pkg <- "yaml"
if (!require(pkg, character.only = TRUE)) {
  install.packages(pkg)
  if (!require(pkg, character.only = TRUE)) stop("load failure: ", pkg)
}

更新.参数化.

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