Question

我有一堆带有envelope元素的XML。每个人的内部都是一个阵列。数组中的每一行都有2个元素。第一个是标识符，第二个是我想要抓取的文本。我需要行的第一个值来标识正确的行，以便我可以获取正确的值。

在下面的例子中，我的行中有'food'，用代码610954表示。我希望在此代码之后抓取2个元素（c('pizza', 'burger')。同样，代码605380表示'饮料'。我想抓住c('coke', 'pepsi')。我怎样才能使用 xml2 包要做到这一点吗？

library(xml2)
library(magrittr)

myxml <- read_xml('
<inside>
 <envelope>
  <card-entries type="array">
     <card-entry>
       <card-id type="integer">605380</card-id>
       <value>coke</value>
     </card-entry>
     <card-entry>
       <card-id type="integer">610954</card-id>
       <value>pizza</value>
     </card-entry>  
   </card-entries>
 </envelope>
 <envelope>
  <card-entries type="array">
     <card-entry>
       <card-id type="integer">605380</card-id>
       <value>pepsi</value>
     </card-entry>
     <card-entry>
       <card-id type="integer">610954</card-id>
       <value>burger</value>
     </card-entry>  
   </card-entries>
 </envelope>
</inside>
'
)

## as far as I can parse it (but not specific enough)
myxml %>%
    xml_find_all('//envelope/card-entries[@type="array"]/card-entry') %>%
    xml_text()

food <- -CODE THAT GIVES HERE c('pizza', 'burger')- # 610954
drinks <- -CODE THAT GIVES HERE c('coke', 'pepsi')- # 605380

Answer 1

您可以像这样修改原始方法来获取饮料：

myxml %>%
  xml_find_all('//envelope/card-entries[@type="array"]/card-entry[card-id = "605380"]/value') %>%
  xml_text()
#[1] "coke"  "pepsi"

但你可以采用其他各种方法

# get following sibling called value
myxml %>% 
  # foods
  xml_find_all('//card-id[text()="610954"]/following-sibling::value') %>%
  xml_text()
#[1] "pizza"  "burger"

# get following::value[1] - Specify [1] or you would get all following values, 
# including "pepsi".  With value[1] you get only the following value.
myxml %>% 
  # foods
  xml_find_all('//card-id[text()="610954"]/following::value[1]') %>%
  xml_text()
#[1] "pizza"  "burger"

# look for value nodes with a preceding sibling with the appropriate card-id
myxml %>% 
  # drinks
  xml_find_all('//value[preceding-sibling::card-id[text()="605380"]]') %>%
  xml_text()
#[1] "coke"  "pepsi"

# Get value node that is a child of card-entry nodes with the appropriate card-id.
# specifically looking in envelope elements
myxml %>% 
  # drinks
  xml_find_all('//envelope/card-entries/card-entry[card-id = "605380"]/value') %>%
  xml_text()
#[1] "coke"  "pepsi"

# less specific
myxml %>% 
  xml_find_all('//card-entry[card-id = "605380"]/value') %>%
  xml_text()
#[1] "coke"  "pepsi"

Answer 2

如下：

library(tidyverse)
library(stringr)
myxml %>%
  xml_find_all('//envelope/card-entries[@type="array"]/card-entry') %>%
  xml_text() %>% 
  map(.f = str_sub, start = c(1, 7), end = c(6, 1000000L)) %>% 
  reduce(rbind) %>% 
  as_tibble() %>% 
  mutate(type = ifelse(V1 == 605380, yes = "drinks", no = "food"))

然后你可以轻松地分别分配饮料和食物。

xml2：在同一行

2 个答案: