多个库中的相同R包

Question

如果一个软件包安装在多个库中会发生什么？例如,在Debian/Ubuntu中,可以通过apt-get安装debianized包,然后直接从CRAN安装相同包的更新版本.使用library()时,是否会加载最新的包,还是依赖于.libPaths()的顺序？

Answer 1

我的理解是它将取决于.libPaths()的顺序.这是来自的代码library

if (!missing(package)) {
        if (is.null(lib.loc)) 
            lib.loc <- .libPaths()
        lib.loc <- lib.loc[file.info(lib.loc)$isdir %in% TRUE]
    #  >>>> snipped code
        newpackage <- is.na(match(pkgname, search()))
        if (newpackage) {
            pkgpath <- find.package(package, lib.loc, quiet = TRUE, 
                verbose = verbose)
            if (length(pkgpath) == 0L) {
          # snipped

这是来自帮助页面 find.package

Details

find.package returns path to the locations where the given packages are found. 
If lib.loc is NULL, then attached packages are searched before the libraries. 
If a package is found more than once, the first match is used. 

如果有多个实例,那么根据我对find.package代码的读取应该有一个警告(除非你将"verbose"设置为FALSE):

if (length(paths) > 1L) {
            paths <- paths[1L]
            if (verbose) 
                warning(gettextf("package %s found more than once,\n
                                 using the one found in %s", 
                  sQuote(pkg), sQuote(paths)), domain = NA)

Answer 2

正如其他人已经说过的那样,.libPaths()搜索顺序问题就是为什么我们设置它以便首先搜索本地包作为发行版本,特别是Debian stable或Ubuntu版本未更新,更有可能更老.

在文件/etc/R/Renviron设置中对此效果有评论:

# edd Apr 2003  Allow local install in /usr/local, also add a directory for
#               Debian packaged CRAN packages, and finally the default dir 
# edd Jul 2007  Now use R_LIBS_SITE, not R_LIBS
R_LIBS_SITE=${R_LIBS_SITE-'/usr/local/lib/R/site-library:/usr/lib/R/site-library:/usr/lib/R/library'}

因此,用户设置的值R_LIBS_SITE将优先,否则使用此处显示的值.