从data.frame获取列名

Question

我有以下代码：

install.packages("XML")
library(XML)
install.packages("plyr")
library(plyr)

feed <- "http://feeds.reuters.com/Reuters/worldNews?format=xml"
reuters<-xmlToList(feed)
data <- lapply(reuters[[1]][names(reuters[[1]])=="item"], data.frame)

data

所有数据都是输出的。

我怎样才能得到所有的title的data？

我尝试过这个names(data)，但它只输出"item" "item" "item"。

Answer 1

您有一个data.frames列表。你可以把它们连在一起：

> names(do.call(rbind.data.frame, data))
[1] "title"           "link"            "description"     "category.text"  
[5] "category..attrs" "pubDate"         "guid.text"       "guid..attrs"    
[9] "origLink"

data1 <- do.call(rbind.data.frame, data)
> head(data1$title)
[1] Niger says will repatriate its illegal migrants from Algeria     
[2] Twin bombing near Kurdish party office in north Iraq kills 30    
[3] Suicide bomber kills four soldiers in Pakistan's tribal northwest
[4] Sisi keeps Egyptian premier to fix economy after turmoil         
[5] Kosovo's Thaci has tough job to form new cabinet, keep promises  
[6] Libyan Supreme Court rules PM's election unconstitutional        
25 Levels: Niger says will repatriate its illegal migrants from Algeria ...

如果你只想要标题

xData <- xmlParse(feed)
> head(xpathSApply(xData, "//title", xmlValue))
[1] "Reuters: World News"                                                 
[2] "Reuters: World News"                                                 
[3] "South Africa platinum strike talks in crucial final day of mediation"
[4] "Africa's sports bars, TV shacks step up security for World Cup"      
[5] "Niger says will repatriate its illegal migrants from Algeria"        
[6] "Twin bombing near Kurdish party office in north Iraq kills 30"     

Answer 2

您还可以只提取名称而不绑定数据帧。

Titles <- character(length(data))
for (i in seq_len(length(data))) Titles[i] <- as.character(data[[i]]$title)
Titles
[1] "Niger says will repatriate its illegal migrants from Algeria"                     "Twin bombing near Kurdish party office in north Iraq kills 30"                   
[3] "Suicide bomber kills four soldiers in Pakistan's tribal northwest"                "Sisi keeps Egyptian premier to fix economy after turmoil"                        
[5] "Kosovo's Thaci has tough job to form new cabinet, keep promises"                  "Libyan Supreme Court rules PM's election unconstitutional"                       
[7] "Thai junta to explain itself to international rights groups"                      "Well-trained and armed, Taliban tried to hijack plane in Pakistan"               
[9] "Russia would react to NATO build-up near borders: minister"                       "Myanmar military 'tortures civilians': human rights group"                       
[11] "Five jailed for killing Russia's Politkovskaya, mastermind unknown" 
...

Answer 3

我通常是这么做的--既快又容易。

unname(sapply(data, '[[', 'title'))

# [1] South Africa platinum strike talks in crucial final day of mediation
# [2] Africa's sports bars, TV shacks step up security for World Cup      
# [3] Niger says will repatriate its illegal migrants from Algeria        
# [4] Twin bombing near Kurdish party office in north Iraq kills 30       
# [5] Suicide bomber kills four soldiers in Pakistan's tribal northwest   
# [6] Sisi keeps Egyptian premier to fix economy after turmoil            
# 25 Levels: South Africa platinum strike talks in crucial final day of mediation ...

您可以类似地访问任何其他元素。

unname(sapply(data, '[[', 'link'))