Question

我可以使用该函数获取所有可用包的列表：

ap <- available.packages()

但是我怎么能从R中获得这些包的描述，所以我可以有一个data.frame有两列：包和描述？

Answer 1

我实际上认为你想要“包”和“标题”作为“描述”可以运行到几行。所以这是前者，如果真的想要“描述”，只需将“描述”放在最后一个子集中：

R> ## from http://developer.r-project.org/CRAN/Scripts/depends.R and adapted
R>
R> require("tools")
R>
R> getPackagesWithTitle <- function() {
+     contrib.url(getOption("repos")["CRAN"], "source") 
+     description <- sprintf("%s/web/packages/packages.rds", 
+                            getOption("repos")["CRAN"])
+     con <- if(substring(description, 1L, 7L) == "file://") {
+         file(description, "rb")
+     } else {
+         url(description, "rb")
+     }
+     on.exit(close(con))
+     db <- readRDS(gzcon(con))
+     rownames(db) <- NULL
+
+     db[, c("Package", "Title")]
+ }
R>
R>
R> head(getPackagesWithTitle())               # I shortened one Title here...
     Package              Title
[1,] "abc"                "Tools for Approximate Bayesian Computation (ABC)"
[2,] "abcdeFBA"           "ABCDE_FBA: A-Biologist-Can-Do-Everything of Flux ..."
[3,] "abd"                "The Analysis of Biological Data"
[4,] "abind"              "Combine multi-dimensional arrays"
[5,] "abn"                "Data Modelling with Additive Bayesian Networks"
[6,] "AcceptanceSampling" "Creation and evaluation of Acceptance Sampling Plans"
R>

Answer 2

Dirk提供了一个非常好的答案，在完成我的解决方案之后，然后看到我辩论了一段时间后发布了我的解决方案，因为害怕看起来很傻。但我决定发布它有两个原因：

开始像我这样的抓手
我花了一段时间才做，所以为什么不这样做:)。

我接近这个想法，我需要做一些网络报废，并选择crantastic作为刮去的网站。首先，我将提供代码，然后提供两个对我有帮助的资源：

library(RCurl)
library(XML)

URL <- "http://cran.r-project.org/web/checks/check_summary.html#summary_by_package"
packs <- na.omit(XML::readHTMLTable(doc = URL, which = 2, header = T, 
    strip.white = T, as.is = FALSE, sep = ",", na.strings = c("999", 
        "NA", " "))[, 1])
Trim <- function(x) {
    gsub("^\\s+|\\s+$", "", x)
}
packs <- unique(Trim(packs))
u1 <- "http://crantastic.org/packages/"
len.samps <- 10 #for demo purpose; use:
#len.samps <- length(packs) # for all of them
URL2 <- paste0(u1, packs[seq_len(len.samps)]) 
scraper <- function(urls){ #function to grab description
    doc   <- htmlTreeParse(urls, useInternalNodes=TRUE)
    nodes <- getNodeSet(doc, "//p")[[3]]
    return(nodes)
}
info <- sapply(seq_along(URL2), function(i) try(scraper(URL2[i]), TRUE))
info2 <- sapply(info, function(x) { #replace errors with NA
        if(class(x)[1] != "XMLInternalElementNode"){
            NA
        } else {
            Trim(gsub("\\s+", " ", xmlValue(x)))
        }
    }
)
pack_n_desc <- data.frame(package=packs[seq_len(len.samps)], 
    description=info2) #make a dataframe of it all

<强>资源：

Answer 3

我想尝试使用HTML抓取工具（rvest）来执行此操作，因为OP中的available.packages()不包含软件包 Descriptions 。 / p>

library('rvest')
url <- 'https://cloud.r-project.org/web/packages/available_packages_by_name.html'
webpage <- read_html(url)
data_html <- html_nodes(webpage,'tr td')
length(data_html)

P1 <- html_nodes(webpage,'td:nth-child(1)') %>% html_text(trim=TRUE)  # XML: The Package Name
P2 <- html_nodes(webpage,'td:nth-child(2)') %>% html_text(trim=TRUE)  # XML: The Description
P1 <- P1[lengths(P1) > 0 & P1 != ""]  # Remove NULL and empty ("") items
length(P1); length(P2);

mdf <- data.frame(P1, P2, row.names=NULL)
colnames(mdf) <- c("PackageName", "Description")

# This is the problem! It lists large sets column-by-column,
# instead of row-by-row. Try with the full list to see what happens.
print(mdf, right=FALSE, row.names=FALSE)

# PackageName Description                                                             
# A3          Accurate, Adaptable, and Accessible Error Metrics for Predictive\nModels
# abbyyR      Access to Abbyy Optical Character Recognition (OCR) API                 
# abc         Tools for Approximate Bayesian Computation (ABC)                        
# abc.data    Data Only: Tools for Approximate Bayesian Computation (ABC)             
# ABC.RAP     Array Based CpG Region Analysis Pipeline                                
# ABCanalysis Computed ABC Analysis

# For small sets we can use either:
# mdf[1:6,] #or# head(mdf, 6)

但是，尽管对于较小的数组/数据框列表（子集）来说效果很好，但我遇到了整个列表的显示问题，其中的数据会以逐列或逐列显示。不结盟。我很高兴能将此 paged 并以某种方式在新窗口中正确设置格式。我尝试使用 page ，但无法使其正常运行。

编辑： 推荐的方法不是上述方法，而是使用Dirk的建议（来自以下注释）：

db <- tools::CRAN_package_db()
colnames(db)
mdf <- data.frame(db[,1], db[,52])
colnames(mdf) <- c("Package", "Description")
print(mdf, right=FALSE, row.names=FALSE)

但是，这仍然遭受提到的显示问题...

从R中列出和描述CRAN中的所有包

3 个答案: