R 语言 - XML 文件
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>