Question

我需要从XML中提取某些看起来像这样的数据（简化为简洁）

<Doc name="Doc1">
    <Lists Count="1">
        <List Name="List1">
            <Points Count="3">
                <Point Id="1">
                    <Tags Count ="1">"a"</Tags>
                    <Point Position="1"  /> 
                </Point>
                <Point Id="2">
                    <Point Position="2"  /> 
                </Point>
                <Point Id="3">
                    <Tags Count="1">"c"</Tags>
                    <Point Position="3"  /> 
                </Point>
            </Points>
        </List>
    </Lists>
</Doc>

输出应该是一个数据框，它将标记和位置与每个点Id

相匹配

    Point  Tag Position
1     1    a        1
2     2 <NA>        2
3     3    c        3

我是XML新手，我正在玩xml2包。到目前为止，我可以单独提取每个变量，但由于某些点可能没有标记数据，我无法找到在三个参数之间进行匹配的方法。

> library(xml2)
> xml_data<-read_xml(...)
> xml_data %>% xml_find_all("//Point") %>% xml_attr("Id")
[1] "1" "2" "3"
> xml_data %>% xml_find_all("//Vertical") %>% xml_attr("Position")
[1] "1" "2" "3"
> xml_data %>% xml_find_all("//Tags") %>% xml_text()
[1] "\"a\"" "\"c\""

Answer 1

purrr和xml2齐聚一堂：

library(xml2)
library(purrr)

txt <- '<Doc name="Doc1">
    <Lists Count="1">
        <List Name="List1">
            <Points Count="3">
                <Point Id="1">
                    <Tags Count ="1">"a"</Tags>
                    <Point Position="1"  /> 
                </Point>
                <Point Id="2">
                    <Point Position="2"  /> 
                </Point>
                <Point Id="3">
                    <Tags Count="1">"c"</Tags>
                    <Point Position="3"  /> 
                </Point>
            </Points>
        </List>
    </Lists>
</Doc>'

doc <- read_xml(txt)
xml_find_all(doc, ".//Points/Point") %>% 
  map_df(function(x) {
    list(
      Point=xml_attr(x, "Id"),
      Tag=xml_find_first(x, ".//Tags") %>%  xml_text() %>%  gsub('^"|"$', "", .),
      Position=xml_find_first(x, ".//Point") %>% xml_attr("Position")
    )
  })
## # A tibble: 3 × 3
##   Point   Tag Position
##   <chr> <chr>    <chr>
## 1     1     a        1
## 2     2  <NA>        2
## 3     3     c        3

Answer 2

在xpathApply个节点上运行//Points/Point，并为每个此类节点x获取Id，Tag（如果没有，则为NA）和{ {1}}：

Position

，并提供：

library(XML)

doc <- xmlTreeParse(Lines, asText = TRUE, useInternalNodes = TRUE)

do.call("rbind", xpathApply(doc, "//Points/Point", function(x) 
  data.frame(Id = as.numeric(xmlAttrs(x)[["Id"]]), 
             Tags = c(gsub('"', '', xmlValue(x[["Tags"]])), NA)[[1]],
             Position = as.numeric(xmlAttrs(x[["Point"]])[["Position"]],
             stringsAsFactors = FALSE))))

<强>变化

以上给出相同答案的变体是这样的。在每个Id Tags Position 1 1 a 1 2 2 <NA> 2 3 3 c 3节点，它创建一个属性和值的字符串，然后使用Point来读取它：

read.table

注意：输入library(XML) doc <- xmlTreeParse(Lines, asText = TRUE, useInternalNodes = TRUE) xp <- xpathSApply(doc, "//Points/Point", function(x) paste( xmlAttrs(x)[["Id"]], c(gsub('"', '', xmlValue(x[["Tags"]])), NA)[[1]], xmlAttrs(x[["Point"]])[["Position"]])) read.table(text = xp, col.names = c("Id", "Tags", "Position"), as.is = TRUE)为：

Lines

从R中的XML中提取数据

2 个答案: