Getting and cleaning data - XML

Question 1

XML THE ESSENTIALS

Question 2

XML ARCHITECTURE

Question 3

XML FIRST STEPS

Answer 3

• library(XML)
• Assign a variable to shorten code lines
  > fileUrl <- “http://www.w3schools.com/xml/simple.xml”
• Load document into memory
  > doc <- xmlTreeParse(fileUrl,useInternal=TRUE)

Question 4

XML EXPLORATION DRILLING

Question 5

XML EXTRACTING DRILLING - 1

Answer 5

• Extract and display 1st section
  > rootNode[[1]]
• Belgian Waffles
  $5.95
  Two of our famous Belgian Waffles with plenty of real*
• maple syrup*
  650

Question 6

XML EXTRACTING DRILLING - 2

Answer 6

• Extract subsection 1 of section 1
  >rootNode[[1]][[1]]
  Belgian Waffles

Question 7

xmlValue

Answer 7

function used to extract value of a named XML node

e.g. xmlSApply(xmlNode[1][1] , xmlValue)

Will extract and display the content of the node corresponding to

subsection 1 of section 1 of the document

Question 8

USING XPATH AS NODE POINTER -1

Answer 8

• nodename Selects all nodes with the name “nodename”
• / Selects from the root node
• // Selects nodes in the document from the current node that
  match the selection no matter where they are
• . Selects the current node
• .. Selects the parent of the current node
• @ Selects attributes

Question 9

USING XPATH AS NODE POINTER -2

Answer 9

• bookstore Selects all nodes with the name “bookstore”
• /bookstore Selects the root element bookstore
• bookstore/book Selects all book elements that are children of bookstore
• //book Selects all book elements no matter where they are in the document
• bookstore//book Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
• //@lang Selects all attributes that are named lang

http://www.w3schools.com/xpath/xpath_syntax.asp

Question 10

USING XPATH AS NODE POINTER -3

Answer 10

• /bookstore/book[1] Selects the first book element that is the child of the bookstore element.
• /bookstore/book[last()-1] Selects the last but one book element that is the child of the bookstore element
• /bookstore/book[position()<3] Selects the first two book elements that are children of the bookstore element
• //title[@lang] Selects all the title elements that have an attribute named lang
• //title[@lang=’en’] Selects all the title elements that have an attribute named lang with a value of ‘en’

Question 11

USING XPATH AS NODE POINTER -4

Answer 11

/bookstore/book[price>35.00] Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00

/bookstore/book[price>35.00]/title Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

/bookstore/* Selects all the child nodes of the bookstore element

//* Selects all elements in the document

//title[@*] Selects all title elements which have any attribute

Question 12

USING XPATH AS NODE POINTER -5

Answer 12

//book/title | //book/price Selects all the title AND price elements of all book elements

//title | //price Selects all the title AND price elements in the document

/bookstore/book/title | //price Selects all the title elements of the book element of the bookstore element AND all the price elements in the document

Question 13

XPATH EXAMPLES

Answer 13

Part of the XML package

xpathSApply(rootNode,”//name”,xmlValue)
[1] “Belgian Waffles” “Strawberry Belgian Waffles” “Berry-Berry Belgian Waffles”
[4] “French Toast” “Homestyle Breakfast”

xpathSApply(rootNode,”//price”,xmlValue)
[1] “$5.95” “$7.95” “$8.95” “$4.50” “$6.95”