10.9.3. Functions

In the previous examples we saw such XPath functions as position( ) and not( ). XPath defines four basic types of functions that return: booleans (true or false), numbers (real numbers), strings (strings of characters), and node-sets. The functions are grouped based on the datatypes they act upon.

The following functions deal with node-sets (optional arguments are followed by a question mark):

last( )

Returns the total number of nodes of which the context node is a part

position( )

Returns a number that is the position of the context node (in document order or after sorting)

count(node-set)

Returns the number of nodes contained in the specified node-set

id(name)

Returns the node with the identifier name

local-name([node-set])

Returns a string that is the name (without the namespace) of the first node in document order of the node-set, or the context-node, if the argument is omitted

namespace-uri([node-set])

Returns a string that is the URI for the namespace of the first node in document order of the node-set, or the context node, if the argument is omitted

name([node-set])

Returns a string that is the full name (with namespace) of the first node in document order of the node-set, or the context node, if the argument is omitted

The following functions deal with strings:

string(object)

Converts its argument object, which can be of any type, to a string.

concat(str1, str2, ...)

Returns the concatenation of its arguments.

starts-with(str1, str2)

Returns true if the first argument string (str1) starts with the second argument string (str2).

contains(str1, str2)

Returns true if the first argument string (str1) contains the second argument string (str2).

substring-before (str1, str2)

Returns the substring of the first argument string (str1) that precedes the first occurrence of the second argument string (str2).

substring-after (str1, str2)

Returns the substring of the first argument string (str1) that follows the first occurrence of the second argument string (str2).

substring(str, num[, length])

Returns the substring of the first argument (str) starting at the position specified by the second argument (num) with the length specified in the third. If the third argument is not specified, the substring continues to the end of the string.

string-length(str)

Returns the number of characters in the string.

normalize-space(str)

Returns the argument string with whitespace normalized by stripping any leading and trailing whitespace and replacing sequences of whitespace characters by a single space.

translate(str1, str2, str3)

Returns the first argument string (str1) with occurrences of characters in the second argument string (str2) replaced by the character at the corresponding position in the third argument string (str3).

The following functions deal with boolean operations:

boolean(object)

Converts its argument (object), which can be of any type, to a boolean

not(boolean)

Returns true if its argument evaluates as false

true( )

Returns true

false( )

Returns false

lang(str)

Returns true if the language of the document (or the closest ancestor indicating the language) is the language passed in the argument (str)

The following functions deal with numbers:

number([obj])

Converts its argument (obj), which can be of any type, to a number (using the context node if the argument is omitted).

sum(node-set)

Returns the sum of the result of converting every node in the node-set to a number. If any node is not a number, the function returns NaN (not a number).

floor(num)

Returns the largest integer that is not greater than the argument (num).

ceiling(num)

Returns the smallest integer that is not less than the argument (num).

round(num)

Returns the integer that is closest to the argument (num).

These functions can be used not only in XPath expressions, but in XSLT elements as well. For example, to count the number of sections in a text, we could add the following to a style sheet:

<xsl:text>The number of sections is </xsl:text>
<xsl:value-of select="count(//section)"/>

10.9.4. Additional XSLT Functions and Types

XSLT defines additional functionality for its own needs. One feature is a new datatype (in addition to the four datatypes defined by XPath): the result tree fragment. This datatype is comparable to a node-set, except that its nodes are in a tree rather than an unorganized collection. All the operations that are permitted for node-sets are permitted for tree fragments. However, you cannot use the /, //, or [ ] operators on result tree fragments.

XSLT also defines additional functions:

document(obj[, node-set])

Returns a node-set that comprises the document whose URI (related to the second, optional argument) was passed as the first argument obj. If the second argument is omitted, the context node is used.

key(str, obj)

Returns the node-set of the nodes keyed by obj in the key named str.

format-number(num, str1[, str2])

Returns a string containing the formatted value of num, according to the format-pattern string in str1 and the decimal-format string in str2 (or the default decimal- format if there is no third argument).

current( )

Returns the current node.

unparsed-entity-uri(str)

Returns the URI of the unparsed entity given by str.

generate-id(node-set)

Generates a unique ID for the first node in the given node-set.

system-property(str)

Returns the value of the system property passed as a string str. The system properties are: xsl:version (the version of XSLT implemented by the processor), xsl:vendor (a string identifying the vendor of the XSL processor), and xsl:vendor-url (the vendor's URL).