Difference between revisions of "Utility Module"

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=Array and Map Functions=
 
=Array and Map Functions=
 
=Helper Functions=
 
  
 
==util:array-members==
 
==util:array-members==
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=Helper Functions=
  
 
==util:replicate==
 
==util:replicate==

Revision as of 09:28, 18 January 2021

This XQuery Module contains various small utility and helper functions. Please note that some of the functions are used for internal query rewritings. They may be renamed or moved to other modules in future versions of BaseX.

Conventions

All functions and errors in this module and errors are assigned to the http://basex.org/modules/util namespace, which is statically bound to the util prefix.

Conditions

util:if

Signatures util:if($condition as item()*, $then as item()*) as item()*
util:if($condition as item()*, $then as item()*, $else as item()*) as item()*
Summary Alternative writing for the if/then/else expression:
  • If the effective boolean value of $condition is true, the $then branch will be evaluated.
  • Otherwise, $else will be evaluated. If no third argument is supplied, an empty sequence will be returned.
Examples
  • util:if(true(), 123, 456) returns 123.
  • util:if(0, 'wrong!') returns an empty sequence.

util:or

Signatures util:or($items as item()*, $default as item()*) as item()*
Summary Returns $items if it is a non-empty sequence. Otherwise, returns $default. The function is equivalent to one of the following expressions:
  • if(exists($items)) then $items else $default
  • $items ?: $default (see Elvis Operator for more details)
Examples
  • util:or(123, 456) returns 123.
  • util:or(1[. = 0], -1) returns -1.

util:within

Template:Mark

Signatures util:within($sequence as item()*, $min as xs:integer) as xs:boolean
util:within($sequence as item()*, $min as xs:integer, $max as xs:integer) as xs:boolean
Summary Checks if the specified $sequence has at least $min and, optionally, at most $max items. Equivalent to let $count := count($sequence) return $count >= $min and $count <= $max.
Examples
  • util:within(('a', 'b', 'c'), 2) returns true.
  • util:within((1 to 1000000000)[. < 10], 3, 6) returns true.

Positional Access

util:item

Signatures util:item($sequence as item()*, $position as xs:double) as item()?
Summary Returns the item from $sequence at the specified $position. Equivalent to $sequence[$position].
Examples
  • util:item(reverse(1 to 5), 1) returns 5.
  • util:item(('a','b'), 0) returns an empty sequence.

util:range

Signatures util:range($sequence as item()*, $first as xs:double, $last as xs:double) as item()*
Summary Returns items from $sequence, starting at position $first and ending at $last. Equivalent to subsequence($sequence, $first, $last - $first + 1).
Examples
  • util:range(//item, 11, 20) returns all path results from (if available) position 11 to 20.

util:last

Signatures util:last($sequence as item()*) as item()?
Summary Returns last item of a $sequence. Equivalent to $sequence[last()].
Examples
  • util:last(reverse(1 to 100)) returns 1.

util:init

Signatures util:init($sequence as item()*) as item()*
Summary Returns all items of a $sequence except for the last one. Equivalent to $sequence[position() < last()].
Examples
  • util:init(1 to 4) returns 1 2 3.

Node Functions

util:ddo

Signatures util:ddo($nodes as node()*) as node()*
Summary Returns nodes in distinct document order: duplicate nodes will be removed, and the remaining nodes will be returned in document order. All results of path expression are in distinct document order, so the function is equivalent to the expression $nodes/self::node().
Signatures util:root($nodes as node()*) as document-node()*
Summary Returns the document nodes of the specified $nodes. The function is equivalent to the expression $nodes ! /. The path expression /abc

is internally represented as util:root(.)/abc</code.

Array and Map Functions

util:array-members

Template:Mark

Signatures util:array-members($array as array(*)) as array(*)*
Summary Returns each member of an $array as a new array. Equivalent to: for $a in 1 to array:size($array) return [ $array($a) ].
Examples
  • Returns three elements with the member values as concatenated text node.

<syntaxhighlight lang="xquery"> let $array := [ (), 2, (3, 4) ] for $member in array:members($array) return element numbers { $member } </syntaxhighlight>

util:array-values

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Signatures util:array-values($array as array(*)) as item()*
Summary Returns all members of an $array as a sequence. Equivalent to *?, but better composable and easier to read.
Examples
  • Returns the array members as two items:

<syntaxhighlight lang="xquery"> let $array := [ (), 2, [ 3, 4 ] ] return array:values($array) </syntaxhighlight>

util:map-entries

Template:Mark

Signatures util:map-entries($map as map(*)) as map(xs:string, item()*)*
Summary Returns each entry (pair) of a $map as a new map with, each with a key and value entry. Equivalent to: map:for-each($map, function($key, $value) { map { "key": $key, "value": $value } }).
Examples
  • Returns three elements named by the key of the map, and with the entries as concatenated text node.

<syntaxhighlight lang="xquery"> let $map := map { 'a': (), 'b': 2, 'c': [ 3, 4 ] } for $entry in map:entries($map) return element { $entry?key } { string-join($entry?value) } </syntaxhighlight>

util:map-values

Template:Mark

Signatures util:map-values($map as map(*)) as item()*
Summary Returns all values of a $map as a sequence. Equivalent to *?, but better composable and easier to read.
Examples
  • Returns the map values as two items:

<syntaxhighlight lang="xquery"> let $map := map { 'a': (), 'b': 2, 'c': [ 3, 4 ] } return map:values($map) </syntaxhighlight>

Helper Functions

util:replicate

Template:Mark Third argument added.

Signatures util:replicate($input as item()*, $count as xs:integer) as item()*
util:replicate($input as item()*, $count as xs:integer, $multiple as xs:boolean) as item()*
Summary Evaluates $input and returns the result $count times. Unless $multiple is enabled, the input expression is only evaluated once. The function call util:replicate($input, $count, true()) is equivalent to (1 to $count) ! $input.
Errors negative: The specified number is negative.
Examples
  • util:replicate('A', 3) returns A A A.
  • In the following query, a single new element node is constructed, and true is returned:

<syntaxhighlight lang="xquery"> let $nodes := util:replicate(<node/>, 2) return $nodes[1] is $nodes[2] </syntaxhighlight>

  • In this query, two nodes are constructed, and the result is false:

<syntaxhighlight lang="xquery"> let $nodes := util:replicate(<node/>, 2, true()) return $nodes[1] is $nodes[2] </syntaxhighlight>

util:intersperse

Template:Mark

Signatures util:intersperse($items as item()*, $separator as item()*) as item()*
Summary Inserts the defined $separator between the $items of a sequence and returns the resulting sequence. The function is equivalent to

head($items), for $item in tail($items) return ($separator, $item)

Examples Inserts semicolon strings between the three input items:

<syntaxhighlight lang="xquery"> fn:intersperse((<_>1</_>, <_>2</_>, <_>3</_>), '; ') </syntaxhighlight>

util:duplicates

Template:Mark

Signatures util:duplicates($sequence as item()*) as xs:anyAtomicType*
util:duplicates($sequence as item()*, $collation as xs:string) as xs:anyAtomicType*
Summary Returns duplicate values in a $sequence. See fn:distinct-values for the applied equality rules and the usage of the $collation argument.
Examples
  • util:duplicates((1, 2, 1, 1)) returns 1.

util:chars

Signatures util:chars($string as xs:string) as xs:string*
Summary Returns all characters of a $string as a sequence. Equivalent to string-to-codepoints($string) ! codepoints-to-string(.).
Examples
  • util:chars('AB') returns the two strings A and B.

Errors

Code Description
negative The specified number is negative.

Changelog

Version 9.5
Version 9.4
Version 9.3
Version 9.2
Version 9.1
Version 9.0

The Module was introduced with Version 8.5.