为什么 rownames(installed.packages()) 有一个名称属性？

我有以下功能供个人使用。它需要输入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))
}

问题就在这里。打开新的 R 会话并分配函数后，第一次调用该函数always返回一个由空字符串组成的字符向量以及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 会话，分配该函数，然后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字符向量......

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

...然后再做一次，它会返回正确的结果...

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

它始终只发生在新 R 会话中的第一次调用时。为什么会发生这种情况？如何修复它，以便该函数在第一次尝试时始终有效？

My R --vanilla会话信息：

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 

Update:打开 R 后，似乎rownames(installed.packages()) has a names属性，因为lme4包裹。不知道为什么，这是唯一的名字。也很奇怪，第二次打电话的时候它就消失了。

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

奇怪，但看起来像rownames(installed.packages()) has a 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" ...

抱歉，这个问题留给你来回答了。只要确保没有名字即可。这对你来说是个问题，因为你依赖sapply的默认值是USE.NAMES=TRUE，但这只会添加尚不存在的名称。他们的出现是出于一些非常奇怪的原因。

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（从开始R --vanilla):

> 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，并且如果我使用，我会一致地得到它们@马丁摩根 https://stackoverflow.com/questions/27116593/why-does-rownamesinstalled-packages-have-a-names-attribute/27116647#comment42737154_27116593的使用建议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