如何将data.table::fread包装在您自己的包中，并具有bit64功能？

Question

我有一个包，其中包含一个函数，该函数从fread调用data.table。data.table在其描述文件的建议字段中包含了bit64包，这使fread能够以integer64而不是numeric的形式导入大整数。在我的包中，默认情况下，我需要这个功能。

下面是一个可重复的例子，在R3.1.3下(早期版本没有这个问题)。

尝试1

Vectorize(dir.create)(c("test", "test/R", "test/man"))

cat(
  "Package: test
Title: Test pkg
Description: Investigate how to use suggested package
Version: 0.0-1
Date: 2015-03-10
Author: Richie Cotton
Maintainer: Richie Cotton <a@b.com>
Imports: data.table
Suggests: bit64
License: Unlimited
",
  file = "test/DESCRIPTION"
)

cat(
  "#' Read data
#' 
#' Wrapper to \\code{fread} that loads bit64 first
#' @param ... Passed to fread.
#' @return A data frame of uniformly distributed random numbers and their index.
#' @importFrom data.table fread
#' @export
read_data <- function(...)
{
  library(bit64)
  fread(...)
}",
  file = "test/R/read_data.R"
)

当我运行R CMD check时

library(roxygen2)
library(devtools)
roxygenize("test")
check("test")

我得到以下NOTE

* checking dependencies in R code ... NOTE
'library' or 'require' call to 'bit64' in package code.
Please use :: or requireNamespace() instead.
See section 'Suggested packages' in the 'Writing R Extensions' manual.

企图2

文档建议用requireNamespace代替library。这将检查包是否存在，但不会将其加载到R的搜索路径。

如果我将read_data的定义更新为：

read_data <- function(...)
{
  if(!requireNamespace('bit64')) 
  {
    warning('bit64 not available.')
  }
  fread(...)
}

然后R CMD check运行得很平稳，但是由于bit64现在没有加载，所以fread无法读取长整数。

尝试3

如果我将DESCRIPTION更改为使bit64位于Depends部分(而不是Suggests )，并将read_data保持在第2次尝试中，或者将其简化为

read_data <- function(...)
{
  fread(...)
}

然后R CMD check给出了NOTE

* checking dependencies in R code ... NOTE
Package in Depends field not imported from: 'bit64'
  These packages need to be imported from (in the NAMESPACE file)
  for when this namespace is loaded but not attached.

我不太确定在这种情况下我应该进口什么。

企图4

如果我将bit64保留在Depends部分，并使用read_data的原始定义，

read_data <- function(...)
{
  library(bit64)
  fread(...)
}

然后R CMD check给出了NOTE

* checking dependencies in R code ... NOTE
'library' or 'require' call to 'bit64' which was already attached by Depends.
Please remove these calls from your code.
Package in Depends field not imported from: 'bit64'

我觉得应该有一些DESCRIPTION和函数定义的神奇组合，它给了我bit64的功能，并且干净地传递了R CMD check；我只是看不出我错过了什么。

我该怎么做？

Answer 1

第3次尝试是最近的；我只是在roxygen文档中需要一个额外的@import bit64。

Vectorize(dir.create)(c("test", "test/R", "test/man"))

cat(
  "Package: test
Title: Test pkg
Description: Investigate how to use suggested package
Version: 0.0-1
Date: 2015-03-10
Author: Richie Cotton
Maintainer: Richie Cotton <a@b.com>
Depends: bit64
Imports: data.table
License: Unlimited
",
  file = "test/DESCRIPTION"
)

cat(
  "#' Read data
#' 
#' Wrapper to \\code{fread} that loads bit64 first
#' @param ... Passed to fread.
#' @return A data frame of uniformly distributed random numbers and their index.
#' @import bit64
#' @importFrom data.table fread
#' @export
read_data <- function(...)
{
  fread(...)
}",
  file = "test/R/read_data.R"
)