Difference between revisions of "Utility Module"
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Revision as of 15:06, 9 March 2023
This XQuery Module contains various utility and helper functions.
For all listed functions, equivalent expressions exist in standard XQuery, but code may be better readable with function calls:
<syntaxhighlight lang="xquery"> (: standard XQuery :) let $result := if(exists($sequence)) then $sequence else ('default', 'values') return $result[last()]
(: XQuery with functions of this module :) $sequence => util:or(('default', 'values')) => util:last() </syntaxhighlight>
In addition, various query optimizations create calls to the utility functions.
Contents
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
Signature | util:if( $condition as item()* $then as item()* $else as item()* := () ) as item()* |
Summary | Alternative writing for the if/then/else expression:
|
Examples |
|
util:or
Signature | util:or( $items as item()* $default as item()* ) as item()* |
Summary | Returns $items if it is a non-empty sequence. Otherwise, returns $default . Equivalent to the following expressions:
<syntaxhighlight lang="xquery"> if(exists($items)) then $items else $default, (: Elvis operator :) $items ?: $default </syntaxhighlight> |
Examples |
|
util:count-within
Updated with BaseX 10: Renamed from util:within
Signature | util:count-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:
<syntaxhighlight lang="xquery"> let $count := count($sequence) return $count >= $min and $count <= $max </syntaxhighlight> |
Examples |
|
Positional Access
util:item
Signature | util:item( $sequence as item()* $position as xs:double ) as item()? |
Summary | Returns the item from $sequence at the specified $position . Equivalent to:
<syntaxhighlight lang="xquery"> $sequence[$position] </syntaxhighlight> |
Examples |
|
util:range
Signature | 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 $last . Equivalent to:
<syntaxhighlight lang="xquery"> subsequence($sequence, $first, $last - $first + 1) </syntaxhighlight> |
Examples |
|
util:last
Signature | util:last( $sequence as item()* ) as item()? |
Summary | Returns last item of a $sequence . Equivalent to:
<syntaxhighlight lang="xquery"> $sequence[last()] </syntaxhighlight> |
Examples |
|
util:init
Signature | util:init( $sequence as item()* ) as item()* |
Summary | Returns all items of a $sequence except for the last one. Equivalent to:
<syntaxhighlight lang="xquery"> $sequence[position() < last()] </syntaxhighlight> |
Examples |
|
Node Functions
util:ddo
Signature | 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. As results of path expressions are brought distinct document order before they are returned, the function is equivalent to:
<syntaxhighlight lang="xquery"> $nodes/self::node() </syntaxhighlight> |
util:root
Signature | util:root( $nodes as node()* ) as document-node()* |
Summary | Returns the document nodes of the specified $nodes . The path expression /abc is internally represented as util:root(.)/abc . Equivalent to:
<syntaxhighlight lang="xquery"> $nodes ! / </syntaxhighlight> |
util:strip-namespaces
Signature | util:strip-namespaces( $node as node() $prefixes as xs:string* := () ) as node() |
Summary | Removes namespaces with the specified $prefixes from the supplied $node . An empty string can be supplied to remove the default namespace. If no prefixes are specified, all namespaces will be removed.
|
Examples |
<syntaxhighlight lang="xquery"> util:strip-namespaces(<xml xmlns='uri' xmlns:prefix='uri2' prefix:name='value'><prefix:child/></xml>) (: yields :) <xml name='value'><child/></xml> </syntaxhighlight>
<syntaxhighlight lang="xquery"> <xml xmlns='uri1'><child xmlns='uri2'/></xml> => util:strip-namespaces() </syntaxhighlight> |
Array and Map Functions
util:array-members
Signature | util:array-members( $array as array(*) ) as array(*)* |
Summary | Returns each member of an $array as a new array. Equivalent to:
<syntaxhighlight lang="xquery"> for $a in 1 to array:size($array) return [ $array($a) ] </syntaxhighlight> |
Examples |
<syntaxhighlight lang="xquery"> let $array := [ (), 2, (3, 4) ] for $member in util:array-members($array) return element numbers { $member } </syntaxhighlight> |
util:array-values
Signature | util:array-values( $array as array(*) ) as item()* |
Summary | Returns all members of an $array as a sequence. Equivalent to:
<syntaxhighlight lang="xquery"> $array ? * </syntaxhighlight> |
Examples |
<syntaxhighlight lang="xquery"> let $array := [ (), 2, [ 3, 4 ] ] return util:array-values($array) </syntaxhighlight> |
util:map-entries
Signature | util:map-entries( $map as map(*) ) as map(xs:string, item()*)* |
Summary | Returns each entry of a $map as a new map, each with a key and value entry. Equivalent to:
<syntaxhighlight lang="xquery"> map:for-each($map, function($key, $value) { map { "key": $key, "value": $value } }) </syntaxhighlight> |
Examples |
<syntaxhighlight lang="xquery"> let $map := map { 'a': (), 'b': 2, 'c': [ 3, 4 ] } for $entry in util:map-entries($map) return element { $entry?key } { string-join($entry?value) } </syntaxhighlight> |
util:map-values
Signature | util:map-values( $map as map(*) ) as item()* |
Summary | Returns all values of a $map as a sequence. Equivalent to:
<syntaxhighlight lang="xquery"> $map ? * </syntaxhighlight> |
Examples |
<syntaxhighlight lang="xquery"> let $map := map { 'a': (), 'b': 2, 'c': [ 3, 4 ] } return util:map-values($map) </syntaxhighlight> |
Helper Functions
util:replicate
Signature | 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 $multiple is enabled, the input expression is only evaluated once. Equivalent expressions:
<syntaxhighlight lang="xquery"> util:replicate($input, $count, true()), (1 to $count) ! $input </syntaxhighlight> |
Errors | negative : The specified number is negative.
|
Examples |
<syntaxhighlight lang="xquery"> let $nodes := util:replicate(<node/>, 2) return $nodes[1] is $nodes[2] </syntaxhighlight>
<syntaxhighlight lang="xquery"> let $nodes := util:replicate(<node/>, 2, true()) return $nodes[1] is $nodes[2] </syntaxhighlight> |
util:intersperse
Signature | util:intersperse( $items as item()* $separator as item()* ) as item()* |
Summary | Inserts the defined $separator between the $items of a sequence and returns the resulting sequence. Equivalent to:
<syntaxhighlight lang="xquery"> head($items), for $item in tail($items) return ($separator, $item) </syntaxhighlight> |
Examples | Inserts semicolon strings between the three input items:
<syntaxhighlight lang="xquery"> fn:intersperse((<_>1</_>, <_>2</_>, <_>3</_>), '; ') </syntaxhighlight> |
util:duplicates
Signature | 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.
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Examples |
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util:chars
Signature | util:chars( $string as xs:string? ) as xs:string* |
Summary | Returns all characters of a $string as a sequence. Equivalent to:
<syntaxhighlight lang="xquery"> for $cp in string-to-codepoints($string) return codepoints-to-string($cp) </syntaxhighlight> |
Examples |
|
Errors
Code | Description |
---|---|
negative
|
The specified number is negative. |
Changelog
- Version 9.7
- Added:
util:strip-namespaces
- Updated:
util:count-within
: Renamed fromutil:within
.
- Version 9.5
- Added:
util:intersperse
,util:within
,util:duplicates
,util:array-members
,util:array-values
,util:map-entries
,util:map-values
- Updated:
util:replicate
: Third argument added.
- Version 9.4
- Added:
util:root
- Version 9.3
- Added:
util:ddo
- Version 9.2
- Added:
util:chars
,util:init
- Updated:
util:item
,util:last
,util:range
renamed (before:util:item-at
,util:item-range
,util:last-from
)
- Version 9.1
- Version 9.0
- Added:
util:replicate
The Module was introduced with Version 8.5.