R：在函数中使用字符向量子集'require'不起作用

Question

为了使我的函数正常工作，我首先需要加载一些包。我想自动加载这个包。也就是说，在代码的第一部分，它将查找所需的包是否已加载，如果尚未加载则加载它。我想到了下面的代码

  #Install and/or load necessary packages
  packages <- c("chron","ncdf","rgdal")
  i.count <- 1
  while (i.count <= length(packages)) {
    if (packages[i.count] %in% rownames(installed.packages()) == FALSE) {
      install.packages(packages[i.count])
      require(packages[i.count])
    } else if (packages[i.count] %in% (.packages()) == FALSE) {
      require(packages[i.count])
    }
    i.count = i.count + 1
  } 

给定上述代码，当运行require(packages[i.count])

行时，我得到以下错误

犯错:

    c("Loading required package: [", "Loading required package: packages", "Loading required package: i.count")
Failed with error:  ‘'package' must be of length 1’
In addition: Warning message:
In if (!loaded) { :
  the condition has length > 1 and only the first element will be used

任何帮助都是感激的。

Answer 1

尝试:

require(packages[i.count],character.only=TRUE)