将变量传递给库函数 [英] Passing variables to the library function

问题描述

package <- c("car","ggplot2","pastecs","psych")
for (i in package){
  if (!(i %in% rownames(installed.packages()))){
    install.packages(i)
  } else{
     print(paste(i,"has been installed"))
     library(i)
     }
 }

我写了一个循环来查看软件包是否已安装，以及是否可用，库应该加载它.

I wrote a loop to see whether the package is installed, and if it is available, the library should load it.

However I got an error: there is no package called 'i'

为什么不能将变量 i 中的值传递给 library 函数?

Why can't I pass the value in variable i to the library function ?

推荐答案

这是您的代码的更简单版本(包含@csgillespie 的建议):

Here's a simpler version of your code (incorporating @csgillespie's suggestion):

p <- c("car","ggplot2","pastecs","psych") 
for(i in seq_along(p)) {
    if(!require(p[i], character.only=TRUE)) {
        install.packages(p[i])
        library(p[i], character.only=TRUE)
    }
}

请注意，由于库和 require 中的非标准评估，您的代码无法正常工作. character.only 参数可解决此问题(根据文档?库):

Note that your code does not work because of non-standard evaluation in library and require. The character.only argument resolves this (per documentation ? library):

character.only
逻辑，表示可以将包或帮助视为字符串.

character.only
a logical indicating whether package or help can be assumed to be character strings.

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