XML是萬(wàn)維網(wǎng)上使用標(biāo)準(zhǔn)ASCII文本，內(nèi)部網(wǎng)和其他地方共享文件格式和數(shù)據(jù)的文件格式。 它代表可擴(kuò)展標(biāo)記語(yǔ)言(XML)。 與HTML類似，它包含標(biāo)記標(biāo)簽。但與標(biāo)記標(biāo)簽描述頁(yè)面結(jié)構(gòu)的HTML不同，標(biāo)記標(biāo)簽描述了文件中包含的數(shù)據(jù)的含義。

可以使用“XML”包讀取R中的xml文件，使用以下命令安裝此軟件包。

install.packages("XML")

準(zhǔn)備XML文件數(shù)據(jù)

通過(guò)將以下數(shù)據(jù)復(fù)制到文本編輯器(如記事本)中來(lái)創(chuàng)建XMl文件。 使用.xml擴(kuò)展名保存文件，并將文件類型選為所有文件(*.*)。創(chuàng)建一個(gè)XML文件：input.xml，內(nèi)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>

讀取XML文件

R使用xmlParse()函數(shù)來(lái)讀取xml文件，它作為列表存儲(chǔ)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)

當(dāng)我們執(zhí)行上述代碼時(shí)，會(huì)產(chǎn)生以下結(jié)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>

獲取XML文件中存在的節(jié)點(diǎn)數(shù)

# 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)

當(dāng)我們執(zhí)行上述代碼時(shí)，會(huì)產(chǎn)生以下結(jié)果 -

output
[1] 8

第一個(gè)節(jié)點(diǎn)的詳細(xì)信息

下面來(lái)看看如何解析文件的第一條記錄，它將給出對(duì)頂級(jí)節(jié)點(diǎn)中存在的各種元素的詳細(xì)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])

當(dāng)我們執(zhí)行上述代碼時(shí)，會(huì)產(chǎn)生以下結(jié)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"

獲取節(jié)點(diǎn)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]])

當(dāng)我們執(zhí)行上述代碼時(shí)，會(huì)產(chǎn)生以下結(jié)果 -

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

XML轉(zhuǎn)到數(shù)據(jù)幀

為了在大文件中有效處理數(shù)據(jù)，我們以xml文件的形式讀取數(shù)據(jù)作為數(shù)據(jù)幀。然后處理數(shù)據(jù)幀進(jìn)行數(shù)據(jù)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)

當(dāng)我們執(zhí)行上述代碼時(shí)，會(huì)產(chǎn)生以下結(jié)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

由于數(shù)據(jù)現(xiàn)在已經(jīng)轉(zhuǎn)為數(shù)據(jù)幀，所以我們可以使用數(shù)據(jù)幀相關(guān)函數(shù)來(lái)讀取和操作文件。