r - 为什么 rownames(installed.packages()) 有 names 属性？

Question

我有以下功能供个人使用。它需要一个作者的名字来查看我的机器上是否有他们的任何软件包。

authoredPackages <- function (author) 
{
    s <- sapply(rownames(installed.packages()), 
        packageDescription, fields = "Author")
    names(grep(author, s, value = TRUE))
}

这就是问题所在。在打开一个新的 R session 并分配函数后，第一次调用函数 总是 返回一个空字符串的字符向量，它是它应该返回的向量的正确长度。要显示这一点，请打开一个新的 R session ，分配函数，并使用您最喜欢的包作者的姓氏运行它。它应该首先返回一个空的字符向量......

authoredPackages("Temple Lang")
# [1] "" "" "" ""

...然后再做一次，它返回正确的结果......

authoredPackages("Temple Lang")
# [1] "jsonlite" "RCurl"    "RJSONIO"  "XML"    

它总是只在新 R session 中的第一次调用时发生。为什么会发生这种情况，我该如何修复它才能使该功能在第一次尝试时始终有效？

我的 R --vanilla session 信息:

R version 3.1.1 (2014-07-10)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base 

更新:打开 R 后，似乎是 rownames(installed.packages())有一个 names属性是因为 lme4包裹。不知道为什么，这是唯一的名字。它在第二次调用时如何消失也很奇怪。

rownames(installed.packages())[228]
#   ret0 
# "lme4"

Answer 1

奇怪，但似乎是 rownames(installed.packages())有一个 names第一次调用它时的属性。

> str(rownames(installed.packages()))
 Named chr [1:125] "bdsmatrix" "bitops" "blotter" "brew" "car" "changepoint" "chron" "colorout" ...
 - attr(*, "names")= chr [1:125] "" "" "" "" ...
> str(rownames(installed.packages()))
 chr [1:125] "bdsmatrix" "bitops" "blotter" "brew" "car" "changepoint" "chron" "colorout" "colorspace" ...

对不起，这让你来回答这个问题。只要确保没有名字。这对您来说是个问题，因为您依赖于 sapply的默认值 USE.NAMES=TRUE ，但这只会在名称不存在的情况下添加名称。他们出现是出于某种非常奇怪的原因。

authoredPackages <- function (author) 
{
    r <- setNames(rownames(installed.packages()), NULL)
    s <- sapply(r, function(x) packageDescription(x)$Author)
    names(grep(author, s, value = TRUE))
}

这是我的 sessionInfo (从 R --vanilla 开始):

> sessionInfo()
R version 3.1.1 (2014-07-10)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] tools_3.1.1

我刚刚升级到 R-3.1.2 并再次尝试。我仍然得到相同的奇怪结果，如果我使用 @MartinMorgan，我会始终如一地得到它们。的建议使用 noCache=TRUE .

> str(rownames(installed.packages(noCache=TRUE)))
 Named chr [1:125] "bdsmatrix" "bitops" "blotter" "brew" "car" "changepoint" "chron" "colorout" ...
 - attr(*, "names")= chr [1:125] "" "" "" "" ...
> str(rownames(installed.packages(noCache=TRUE)))
 Named chr [1:125] "bdsmatrix" "bitops" "blotter" "brew" "car" "changepoint" "chron" "colorout" ...
 - attr(*, "names")= chr [1:125] "" "" "" "" ...
> str(rownames(installed.packages(noCache=TRUE)))
 Named chr [1:125] "bdsmatrix" "bitops" "blotter" "brew" "car" "changepoint" "chron" "colorout" ...
 - attr(*, "names")= chr [1:125] "" "" "" "" ...
> sessionInfo()
R version 3.1.2 (2014-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] setwidth_1.0-3 colorout_1.0-1

loaded via a namespace (and not attached):
[1] tools_3.1.2