XPath Functions

XPath Function Categories

XPath provides built-in functions for string manipulation, numeric calculations, node operations, and boolean logic. These functions enable powerful queries and data transformations directly within XPath expressions.

concat(), substring(), contains()

sum(), count(), round()

name(), position(), last()

not(), true(), false()

🔹 Basic XPath Syntax

Understanding XPath path expressions:

<!-- Sample XML -->
<bookstore>
    <book category="fiction">
        <title>The Great Gatsby</title>
        <price>10.99</price>
    </book>
    <book category="science">
        <title>Physics 101</title>
        <price>35.00</price>
    </book>
</bookstore>

// Select all books
/bookstore/book

// Select all titles
//title

// Select first book
/bookstore/book[1]

// Select books with price > 20
//book[price>20]

// Select fiction books
//book[@category='fiction']

🔹 String Functions

Common string manipulation functions:

🔸 concat() - Combine Strings

// Combine first and last name
concat(firstname, ' ', lastname)

// Result: "John Doe"

🔸 substring() - Extract Text

// Get first 5 characters
substring(title, 1, 5)

// From "The Great Gatsby" → "The G"

🔸 contains() - Check Text

// Find books with "XML" in title
//book[contains(title, 'XML')]

🔸 string-length() - Get Length

// Get title length
string-length(title)

// "The Great Gatsby" → 16

🔸 starts-with() - Check Start

// Books starting with "The"
//book[starts-with(title, 'The')]

🔸 translate() - Replace Characters

// Convert to uppercase
translate(title, 'abc', 'ABC')

🔹 Numeric Functions

Functions for working with numbers:

🔸 count() - Count Nodes

// Count all books
count(//book)

// Count fiction books
count(//book[@category='fiction'])

🔸 sum() - Add Values

// Total price of all books
sum(//book/price)

// Result: 45.99

🔸 round() - Round Numbers

// Round price
round(price)

// 10.99 → 11

🔸 floor() and ceiling()

// Round down
floor(10.99)  // Result: 10

// Round up
ceiling(10.01)  // Result: 11

🔸 number() - Convert to Number

// Convert string to number
number('123')  // Result: 123

🔹 Node Functions

Functions for working with nodes:

🔸 position() - Get Position

// Select first 3 books
//book[position() <= 3]

// Select even-positioned books
//book[position() mod 2 = 0]

🔸 last() - Get Last Position

// Select last book
//book[last()]

// Select last 2 books
//book[position() > last()-2]

🔸 name() - Get Element Name

// Get element name
name(//book[1])  // Result: "book"

🔸 local-name() - Get Local Name

// Get name without namespace
local-name(//book[1])

🔹 Boolean Functions

Logical operations in XPath:

🔸 not() - Negate Condition

// Books NOT in fiction category
//book[not(@category='fiction')]

🔸 true() and false()

// Always true
//book[true()]

// Always false
//book[false()]

🔸 boolean() - Convert to Boolean

// Check if element exists
boolean(//book/author)

🔹 XPath Operators

Combine conditions with operators:

// AND operator
//book[price>20 and @category='fiction']

// OR operator
//book[price<15 or price>40]

// Comparison operators
//book[price = 10.99]
//book[price != 10.99]
//book[price < 20]
//book[price > 20]
//book[price <= 20]
//book[price >= 20]

// Math operators
//book[price + 5 > 30]
//book[price * 2 < 50]

🔹 XPath Axes

Navigate relationships between nodes:

// Child axis (default)
/bookstore/child::book

// Descendant axis
//descendant::title

// Parent axis
//title/parent::book

// Ancestor axis
//price/ancestor::bookstore

// Following-sibling
//book[1]/following-sibling::book

// Preceding-sibling
//book[2]/preceding-sibling::book

// Attribute axis
//book/attribute::category

🔹 Using XPath in JavaScript

Evaluate XPath expressions in the browser:

const xmlString = `
<bookstore>
    <book>
        <title>XML Guide</title>
        <price>29.99</price>
    </book>
</bookstore>
`;

const parser = new DOMParser();
const xmlDoc = parser.parseFromString(xmlString, "text/xml");

// Evaluate XPath
const result = xmlDoc.evaluate(
    "//book/title",
    xmlDoc,
    null,
    XPathResult.STRING_TYPE,
    null
);

console.log(result.stringValue); // Output: XML Guide

🔹 Advanced XPath Examples

Complex queries combining multiple functions:

// Books with titles longer than 10 characters
//book[string-length(title) > 10]

// Books in positions 2 to 4
//book[position() >= 2 and position() <= 4]

// Books with price between 20 and 40
//book[price >= 20 and price <= 40]

// Count expensive books
count(//book[price > 30])

// Average price (using sum and count)
sum(//book/price) div count(//book)

// Books with "Guide" in title (case-insensitive)
//book[contains(translate(title, 'GUIDE', 'guide'), 'guide')]