R语言XML文件

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2023-03-14

XML是万维网上使用标准ASCII文本，内部网和其他地方共享文件格式和数据的文件格式。它代表可扩展标记语言(XML)。与HTML类似，它包含标记标签。但与标记标签描述页面结构的HTML不同，标记标签描述了文件中包含的数据的含义。

可以使用“XML”包读取R中的xml文件，使用以下命令安装此软件包。

install.packages("XML")

准备XML文件数据

通过将以下数据复制到文本编辑器(如记事本)中来创建XMl文件。使用.xml扩展名保存文件，并将文件类型选为所有文件(*.*)。创建一个XML文件：input.xml，内容如下 -

<RECORDS>
   <EMPLOYEE>
      <ID>1</ID>
      <NAME>Rick</NAME>
      <SALARY>623.3</SALARY>
      <STARTDATE>1/1/2012</STARTDATE>
      <DEPT>IT</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>2</ID>
      <NAME>Dan</NAME>
      <SALARY>515.2</SALARY>
      <STARTDATE>9/23/2013</STARTDATE>
      <DEPT>Operations</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>3</ID>
      <NAME>Michelle</NAME>
      <SALARY>611</SALARY>
      <STARTDATE>11/15/2014</STARTDATE>
      <DEPT>IT</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>4</ID>
      <NAME>Ryan</NAME>
      <SALARY>729</SALARY>
      <STARTDATE>5/11/2014</STARTDATE>
      <DEPT>HR</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>5</ID>
      <NAME>Gary</NAME>
      <SALARY>843.25</SALARY>
      <STARTDATE>3/27/2015</STARTDATE>
      <DEPT>Finance</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>6</ID>
      <NAME>Nina</NAME>
      <SALARY>578</SALARY>
      <STARTDATE>5/21/2013</STARTDATE>
      <DEPT>IT</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>7</ID>
      <NAME>Simon</NAME>
      <SALARY>632.8</SALARY>
      <STARTDATE>7/30/2013</STARTDATE>
      <DEPT>Operations</DEPT>
   </EMPLOYEE>

   <EMPLOYEE>
      <ID>8</ID>
      <NAME>Guru</NAME>
      <SALARY>722.5</SALARY>
      <STARTDATE>6/17/2014</STARTDATE>
      <DEPT>Finance</DEPT>
   </EMPLOYEE>

</RECORDS>

读取XML文件

R使用xmlParse()函数来读取xml文件，它作为列表存储在R中。

# Load the package required to read XML files.
library("XML")

# Also load the other required package.
library("methods")

# Give the input file name to the function.
result <- xmlParse(file = "input.xml")

# Print the result.
print(result)

当我们执行上述代码时，会产生以下结果 -

<?xml version="1.0"?>
<RECORDS>
  <EMPLOYEE>
    <ID>1</ID>
    <NAME>Rick</NAME>
    <SALARY>623.3</SALARY>
    <STARTDATE>1/1/2012</STARTDATE>
    <DEPT>IT</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>2</ID>
    <NAME>Dan</NAME>
    <SALARY>515.2</SALARY>
    <STARTDATE>9/23/2013</STARTDATE>
    <DEPT>Operations</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>3</ID>
    <NAME>Michelle</NAME>
    <SALARY>611</SALARY>
    <STARTDATE>11/15/2014</STARTDATE>
    <DEPT>IT</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>4</ID>
    <NAME>Ryan</NAME>
    <SALARY>729</SALARY>
    <STARTDATE>5/11/2014</STARTDATE>
    <DEPT>HR</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>5</ID>
    <NAME>Gary</NAME>
    <SALARY>843.25</SALARY>
    <STARTDATE>3/27/2015</STARTDATE>
    <DEPT>Finance</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>6</ID>
    <NAME>Nina</NAME>
    <SALARY>578</SALARY>
    <STARTDATE>5/21/2013</STARTDATE>
    <DEPT>IT</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>7</ID>
    <NAME>Simon</NAME>
    <SALARY>632.8</SALARY>
    <STARTDATE>7/30/2013</STARTDATE>
    <DEPT>Operations</DEPT>
  </EMPLOYEE>
  <EMPLOYEE>
    <ID>8</ID>
    <NAME>Guru</NAME>
    <SALARY>722.5</SALARY>
    <STARTDATE>6/17/2014</STARTDATE>
    <DEPT>Finance</DEPT>
  </EMPLOYEE>
</RECORDS>

获取XML文件中存在的节点数

# Load the packages required to read XML files.
library("XML")
library("methods")

# Give the input file name to the function.
result <- xmlParse(file = "input.xml")

# Exract the root node form the xml file.
rootnode <- xmlRoot(result)

# Find number of nodes in the root.
rootsize <- xmlSize(rootnode)

# Print the result.
print(rootsize)

当我们执行上述代码时，会产生以下结果 -

output
[1] 8

第一个节点的详细信息

下面来看看如何解析文件的第一条记录，它将给出对顶级节点中存在的各种元素的详细信息。

# Load the packages required to read XML files.
library("XML")
library("methods")

# Give the input file name to the function.
result <- xmlParse(file = "input.xml")

# Exract the root node form the xml file.
rootnode <- xmlRoot(result)

# Print the result.
print(rootnode[1])

当我们执行上述代码时，会产生以下结果 -

$EMPLOYEE
<EMPLOYEE>
  <ID>1</ID>
  <NAME>Rick</NAME>
  <SALARY>623.3</SALARY>
  <STARTDATE>1/1/2012</STARTDATE>
  <DEPT>IT</DEPT>
</EMPLOYEE> 

attr(,"class")
[1] "XMLInternalNodeList" "XMLNodeList"

获取节点的其它元素

# Load the packages required to read XML files.
library("XML")
library("methods")

# Give the input file name to the function.
result <- xmlParse(file = "input.xml")

# Exract the root node form the xml file.
rootnode <- xmlRoot(result)

# Get the first element of the first node.
print(rootnode[[1]][[1]])

# Get the fifth element of the first node.
print(rootnode[[1]][[5]])

# Get the second element of the third node.
print(rootnode[[3]][[2]])

当我们执行上述代码时，会产生以下结果 -

<ID>1</ID> 
<DEPT>IT</DEPT> 
<NAME>Michelle</NAME>

XML转到数据帧

为了在大文件中有效处理数据，我们以xml文件的形式读取数据作为数据帧。然后处理数据帧进行数据分析。

# Load the packages required to read XML files.
library("XML")
library("methods")

# Convert the input xml file to a data frame.
xmldataframe <- xmlToDataFrame("input.xml")
print(xmldataframe)

当我们执行上述代码时，会产生以下结果 -

  ID     NAME SALARY  STARTDATE       DEPT
1  1     Rick  623.3   1/1/2012         IT
2  2      Dan  515.2  9/23/2013 Operations
3  3 Michelle    611 11/15/2014         IT
4  4     Ryan    729  5/11/2014         HR
5  5     Gary 843.25  3/27/2015    Finance
6  6     Nina    578  5/21/2013         IT
7  7    Simon  632.8  7/30/2013 Operations
8  8     Guru  722.5  6/17/2014    Finance

由于数据现在已经转为数据帧，所以我们可以使用数据帧相关函数来读取和操作文件。