Question

我有以下功能供个人使用。它需要一个作者的名字才能看到我的机器上是否有任何包装。

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

这是问题所在。在打开一个新的R会话并分配该函数时，对函数的总是的第一次调用返回一个空字符串的字符向量，它应该返回它的向量的正确长度。要显示此信息，请打开一个新的R会话，分配该功能，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字符向量...

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

...然后再次执行并返回正确的结果......

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

它始终只发生在新R会话的第一次呼叫中。为什么会发生这种情况，如何解决这个问题，以便第一次尝试使用该功能？

我的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

更新：在打开R时，由于rownames(installed.packages())包，似乎names具有lme4属性。不知道为什么，这是唯一的名字。它在第二次通话中消失的方式也很奇怪。

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

Answer 1

奇怪，但似乎rownames(installed.packages())在您第一次调用它时具有names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，这让你回答这个问题。只要确保没有名字。这对您来说是一个问题，因为您依赖于sapply的默认值USE.NAMES=TRUE，但只会添加名称（如果它们尚未存在）。而且出于某些非常奇怪的原因，他们出现了。

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的建议使用noCache=TRUE，我会始终如一地得到它们。

> 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

为什么rownames（installed.packages（））具有names属性？

1 个答案: