R Read and Write XML Files

Introduction

XML (eXtensible Markup Language) is a widely-used format for storing and exchanging structured data. In R, you can read from and write to XML files using the XML package. This package provides functions to parse, generate, and manipulate XML data efficiently.

Installing and Loading the XML Package

First, you need to install and load the XML package. You can install it from CRAN using the install.packages() function.

Installing the Package

# Install the XML package
install.packages("XML")

Loading the Package

# Load the XML package
library(XML)

Reading XML Files

You can read XML files in R using the xmlTreeParse() function from the XML package. This function reads an XML file and creates an R object that represents the XML structure.

Example: Reading an XML File

Example:

# Sample XML content saved in a file named "sample_data.xml"
# <data>
#   <person>
#     <Name>Alice</Name>
#     <Age>30</Age>
#     <Gender>F</Gender>
#     <Salary>50000</Salary>
#   </person>
#   <person>
#     <Name>Bob</Name>
#     <Age>25</Age>
#     <Gender>M</Gender>
#     <Salary>45000</Salary>
#   </person>
#   <!-- Additional person entries -->
# </data>

# Reading an XML file
xml_data <- xmlTreeParse("sample_data.xml", useInternalNodes = TRUE)
root_node <- xmlRoot(xml_data)
print(root_node)

# Extracting data
names <- xpathSApply(root_node, "//Name", xmlValue)
ages <- xpathSApply(root_node, "//Age", xmlValue)
genders <- xpathSApply(root_node, "//Gender", xmlValue)
salaries <- xpathSApply(root_node, "//Salary", xmlValue)

# Creating a data frame
data <- data.frame(Name = names, Age = as.numeric(ages), Gender = genders, Salary = as.numeric(salaries))
print(data)

Writing to XML Files

You can write data to XML files in R using the saveXML() function from the XML package. This function writes an XML document to a file.

Example: Writing to an XML File

Example:

# Creating a new XML document
doc <- newXMLDoc()
root <- newXMLNode("data", doc = doc)

# Adding data to the XML document
newXMLNode("person",
           newXMLNode("Name", "Alice"),
           newXMLNode("Age", "30"),
           newXMLNode("Gender", "F"),
           newXMLNode("Salary", "50000"),
           parent = root)

newXMLNode("person",
           newXMLNode("Name", "Bob"),
           newXMLNode("Age", "25"),
           newXMLNode("Gender", "M"),
           newXMLNode("Salary", "45000"),
           parent = root)

# Writing the XML document to a file
saveXML(doc, file = "output_data.xml")

Writing a Data Frame to an XML File

You can write a data frame to an XML file by converting each row of the data frame into XML nodes.

Example:

# Creating a data frame
data <- data.frame(
  Name = c("Alice", "Bob", "Charlie", "Diana", "Eve"),
  Age = c(30, 25, 35, 28, 40),
  Gender = c("F", "M", "M", "F", "F"),
  Salary = c(50000, 45000, 55000, 48000, 60000)
)

# Creating a new XML document
doc <- newXMLDoc()
root <- newXMLNode("data", doc = doc)

# Adding data frame rows to the XML document
for (i in 1:nrow(data)) {
  person <- newXMLNode("person", parent = root)
  newXMLNode("Name", data$Name[i], parent = person)
  newXMLNode("Age", data$Age[i], parent = person)
  newXMLNode("Gender", data$Gender[i], parent = person)
  newXMLNode("Salary", data$Salary[i], parent = person)
}

# Writing the XML document to a file
saveXML(doc, file = "output_dataframe.xml")

Example Program Using XML Files

Here is an example program that demonstrates the reading and writing of XML files in R using the XML package, including writing a data frame to an XML file.

Example Program

# R Program to Demonstrate Reading and Writing XML Files

# Install and load the necessary package
install.packages("XML")
library(XML)

# Sample XML content saved in a file named "sample_data.xml"
# <data>
#   <person>
#     <Name>Alice</Name>
#     <Age>30</Age>
#     <Gender>F</Gender>
#     <Salary>50000</Salary>
#   </person>
#   <person>
#     <Name>Bob</Name>
#     <Age>25</Age>
#     <Gender>M</Gender>
#     <Salary>45000</Salary>
#   </person>
#   <!-- Additional person entries -->
# </data>

# Reading an XML file
xml_data <- xmlTreeParse("sample_data.xml", useInternalNodes = TRUE)
root_node <- xmlRoot(xml_data)
print("Root Node of XML Document:")
print(root_node)

# Extracting data from the XML document
names <- xpathSApply(root_node, "//Name", xmlValue)
ages <- xpathSApply(root_node, "//Age", xmlValue)
genders <- xpathSApply(root_node, "//Gender", xmlValue)
salaries <- xpathSApply(root_node, "//Salary", xmlValue)

# Creating a data frame from the extracted data
data <- data.frame(Name = names, Age = as.numeric(ages), Gender = genders, Salary = as.numeric(salaries))
print("Data Frame Created from XML Data:")
print(data)

# Creating a new XML document
doc <- newXMLDoc()
root <- newXMLNode("data", doc = doc)

# Adding data to the XML document
newXMLNode("person",
           newXMLNode("Name", "Alice"),
           newXMLNode("Age", "30"),
           newXMLNode("Gender", "F"),
           newXMLNode("Salary", "50000"),
           parent = root)

newXMLNode("person",
           newXMLNode("Name", "Bob"),
           newXMLNode("Age", "25"),
           newXMLNode("Gender", "M"),
           newXMLNode("Salary", "45000"),
           parent = root)

# Writing the XML document to a file
saveXML(doc, file = "output_data.xml")
print("Data written to output_data.xml")

# Writing a data frame to an XML file

# Creating a data frame
data <- data.frame(
  Name = c("Alice", "Bob", "Charlie", "Diana", "Eve"),
  Age = c(30, 25, 35, 28, 40),
  Gender = c("F", "M", "M", "F", "F"),
  Salary = c(50000, 45000, 55000, 48000, 60000)
)

# Creating a new XML document
doc <- newXMLDoc()
root <- newXMLNode("data", doc = doc)

# Adding data frame rows to the XML document
for (i in 1:nrow(data)) {
  person <- newXMLNode("person", parent = root)
  newXMLNode("Name", data$Name[i], parent = person)
  newXMLNode("Age", data$Age[i], parent = person)
  newXMLNode("Gender", data$Gender[i], parent = person)
  newXMLNode("Salary", data$Salary[i], parent = person)
}

# Writing the XML document to a file
saveXML(doc, file = "output_dataframe.xml")
print("Data frame written to output_dataframe.xml")

Conclusion

In this chapter, you learned how to read from and write to XML files in R using the XML package. XML is a popular format for storing and exchanging structured data, and being able to work with it is essential for data analysis and web applications. You also learned how to write a data frame to an XML file. By mastering these functions, you can efficiently handle XML data in your R programs.