Difference between revisions of "Utility Module"

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This [[Module Library|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.
+
This [[Module Library|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.
  
 
=Conventions=
 
=Conventions=
Line 33: Line 48:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns {{Code|$items}} if it is a non-empty sequence. Otherwise, returns {{Code|$default}}. The function is equivalent to one of the following expressions:
+
|Returns {{Code|$items}} if it is a non-empty sequence. Otherwise, returns {{Code|$default}}. Equivalent to the following expressions:
* <code>if(exists($items)) then $items else $default</code>
+
<syntaxhighlight lang="xquery">
* <code>$items ?: $default</code> (see [[XQuery Extensions#Elvis Operator|Elvis Operator]] for more details)
+
if(exists($items)) then $items else $default,
 +
(: Elvis operator :)
 +
$items ?: $default
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 41: Line 59:
 
* <code>util:or(123, 456)</code> returns {{Code|123}}.
 
* <code>util:or(123, 456)</code> returns {{Code|123}}.
 
* <code>util:or(1[. = 0], -1)</code> returns {{Code|-1}}.
 
* <code>util:or(1[. = 0], -1)</code> returns {{Code|-1}}.
 +
|}
 +
 +
==util:within==
 +
 +
{{Mark|Introduced with Version 9.5:}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:within|$sequence as item()*, $min as xs:integer|xs:boolean}}<br/>{{Func|util:within|$sequence as item()*, $min as xs:integer, $max as xs:integer|xs:boolean}}
 +
|-
 +
| '''Summary'''
 +
|Checks if the specified {{Code|$sequence}} has at least {{Code|$min}} and, optionally, at most {{Code|$max}} items. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
let $count := count($sequence)
 +
return $count >= $min and $count <= $max
 +
</syntaxhighlight>
 +
|-
 +
| '''Examples'''
 +
|
 +
* <code>util:within(('a', 'b', 'c'), 2)</code> returns {{Code|true}}.
 +
* <code>util:within((1 to 1000000000)[. < 10], 3, 6)</code> returns {{Code|true}}.
 
|}
 
|}
  
Line 53: Line 93:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns the item from {{Code|$sequence}} at the specified {{Code|$position}}. Equivalent to <code>$sequence[$position]</code>.
+
|Returns the item from {{Code|$sequence}} at the specified {{Code|$position}}. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
$sequence[$position]
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 69: Line 112:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns items from {{Code|$sequence}}, starting at position {{Code|$first}} and ending at {{Code|$last}}. Equivalent to <code>subsequence($sequence, $first, $last - $first + 1)</code>.
+
|Returns items from {{Code|$sequence}}, starting at position {{Code|$first}} and ending at {{Code|$last}}. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
subsequence($sequence, $first, $last - $first + 1)
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 84: Line 130:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns last item of a {{Code|$sequence}}. Equivalent to <code>$sequence[last()]</code>.
+
|Returns last item of a {{Code|$sequence}}. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
$sequence[last()]
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 99: Line 148:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns all items of a {{Code|$sequence}} except for the last one. Equivalent to <code>$sequence[position() < last()]</code>.
+
|Returns all items of a {{Code|$sequence}} except for the last one. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
$sequence[position() < last()]
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 116: Line 168:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns nodes in ''distinct document order'': duplicate nodes will be removed, and the remaining nodes will be returned in [https://www.w3.org/TR/xquery-31/#dt-document-order document order]. All results of path expression are in distinct document order, so the function is equivalent to the expression <code>$nodes/self::node()</code>.
+
|Returns nodes in ''distinct document order'': duplicate nodes will be removed, and the remaining nodes will be returned in [https://www.w3.org/TR/xquery-31/#dt-document-order 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>
 
|}
 
|}
  
{{Mark|Introduced with Version 9.4:}}
+
==util:root==
  
 
{| width='100%'
 
{| width='100%'
Line 127: Line 182:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns the document nodes of the specified {{Code|$nodes}}. The function is equivalent to the expression <code>$nodes ! /</code>. The path expression <code>/abc</code>
+
|Returns the document nodes of the specified {{Code|$nodes}}. The path expression <code>/abc</code> is internally represented as <code>util:root(.)/abc</code. Equivalent to:
is internally represented as <code>util:root(.)/abc</code.
+
<syntaxhighlight lang="xquery">
 +
$nodes ! /
 +
</syntaxhighlight>
 +
|}
 +
 
 +
=Array and Map Functions=
 +
 
 +
==util:array-members==
 +
 
 +
{{Mark|Introduced with Version 9.5.}}
  
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:array-members|$array as array(*)|array(*)*}}
 +
|-
 +
| '''Summary'''
 +
|Returns each member of an {{Code|$array}} as a new array. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
for $a in 1 to array:size($array)
 +
return [ $array($a) ]
 +
</syntaxhighlight>
 +
|-
 +
| '''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 { $member }
 +
</syntaxhighlight>
 +
|}
 +
 +
==util:array-values==
 +
 +
{{Mark|Introduced with Version 9.5.}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:array-values|$array as array(*)|item()*}}
 +
|-
 +
| '''Summary'''
 +
|Returns all members of an {{Code|$array}} as a sequence. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
$array ? *
 +
</syntaxhighlight>
 +
|-
 +
| '''Examples'''
 +
|
 +
* Returns the array members as two items:
 +
<syntaxhighlight lang="xquery">
 +
let $array := [ (), 2, [ 3, 4 ] ]
 +
return array:values($array)
 +
</syntaxhighlight>
 +
|}
 +
 +
==util:map-entries==
 +
 +
{{Mark|Introduced with Version 9.5.}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:map-entries|$map as map(*)|map(xs:string, item()*)*}}
 +
|-
 +
| '''Summary'''
 +
|Returns each entry of a {{Code|$map}} as a new map, each with a {{Code|key}} and {{Code|value}} entry. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
map:for-each($map, function($key, $value) {
 +
  map { "key": $key, "value": $value }
 +
})
 +
</syntaxhighlight>
 +
|-
 +
| '''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==
 +
 +
{{Mark|Introduced with Version 9.5.}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:map-values|$map as map(*)|item()*}}
 +
|-
 +
| '''Summary'''
 +
|Returns all values of a {{Code|$map}} as a sequence. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
$map ? *
 +
</syntaxhighlight>
 +
|-
 +
| '''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>
 
|}
 
|}
  
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|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Evaluates {{Code|$input}} and returns the result {{Code|$count}} times. Unless {{Code|$multiple}} is enabled, the input expression is only evaluated once. The function call <code>util:replicate($input, $count, true())</code> is equivalent to <code>(1 to $count) ! $input</code>.
+
|Evaluates {{Code|$input}} and returns the result {{Code|$count}} times. Unless {{Code|$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'''
 
| '''Errors'''
Line 162: Line 325:
 
return $nodes[1] is $nodes[2]
 
return $nodes[1] is $nodes[2]
 
</syntaxhighlight>
 
</syntaxhighlight>
 +
|}
 +
 +
==util:intersperse==
 +
 +
{{Mark|Introduced with Version 9.5.}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:intersperse|$items as item()*, $separator as item()*|item()*}}
 +
|-
 +
| '''Summary'''
 +
|Inserts the defined {{Code|$separator}} between the {{Code|$items}} of a sequence and returns the resulting sequence. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
head($items), for $item in tail($items) return ($separator, $item)
 +
</syntaxhighlight>
 +
|-
 +
| '''Examples'''
 +
| Inserts semicolon strings between the three input items:
 +
<syntaxhighlight lang="xquery">
 +
fn:intersperse((<_>1</_>, <_>2</_>, <_>3</_>), '; ')
 +
</syntaxhighlight>
 +
|}
 +
 +
==util:duplicates==
 +
 +
{{Mark|Introduced with Version 9.5.}}
 +
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|util:duplicates|$sequence as item()*|xs:anyAtomicType*}}<br/>{{Func|util:duplicates|$sequence as item()*, $collation as xs:string|xs:anyAtomicType*}}
 +
|-
 +
| '''Summary'''
 +
|Returns duplicate values in a {{Code|$sequence}}. See [https://www.w3.org/TR/xpath-functions-31/#func-distinct-values fn:distinct-values] for the applied equality rules and the usage of the {{Code|$collation}} argument.
 +
|-
 +
| '''Examples'''
 +
|
 +
* <code>util:duplicates((1, 2, 1, 1))</code> returns <code>1</code>.
 
|}
 
|}
  
Line 172: Line 374:
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Returns all characters of a {{Code|$string}} as a sequence. Equivalent to <code>string-to-codepoints($string) ! codepoints-to-string(.)</code>.
+
|Returns all characters of a {{Code|$string}} as a sequence. Equivalent to:
 +
<syntaxhighlight lang="xquery">
 +
for $cp in string-to-codepoints($string)
 +
return codepoints-to-string($cp)
 +
</syntaxhighlight>
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
Line 192: Line 398:
  
 
;Version 9.5
 
;Version 9.5
 +
* Added: [[#util:intersperse|util:intersperse]], [[#util:within|util:within]], [[#util:duplicates|util:duplicates]], [[#util:array-members|util:array-members]], [[#util:array-values|util:array-values]], [[#util:map-entries|util:map-entries]], [[#util:map-values|util:map-values]]
 
* Updated: [[#util:replicate|util:replicate]]: Third argument added.
 
* Updated: [[#util:replicate|util:replicate]]: Third argument added.
  

Revision as of 11:17, 25 February 2021

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.

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. Equivalent to the following expressions:

<syntaxhighlight lang="xquery"> if(exists($items)) then $items else $default, (: Elvis operator :) $items ?: $default </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> let $count := count($sequence) return $count >= $min and $count <= $max </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> $sequence[$position] </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> subsequence($sequence, $first, $last - $first + 1) </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> $sequence[last()] </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> $sequence[position() < last()] </syntaxhighlight>

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. 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

Signatures 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</code. Equivalent to:

<syntaxhighlight lang="xquery"> $nodes ! / </syntaxhighlight>

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:

<syntaxhighlight lang="xquery"> for $a in 1 to array:size($array) return [ $array($a) ] </syntaxhighlight>

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

Template:Mark

Signatures 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
  • 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 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
  • 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:

<syntaxhighlight lang="xquery"> $map ? * </syntaxhighlight>

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. Equivalent expressions:

<syntaxhighlight lang="xquery"> util:replicate($input, $count, true()), (1 to $count) ! $input </syntaxhighlight>

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. 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

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:

<syntaxhighlight lang="xquery"> for $cp in string-to-codepoints($string) return codepoints-to-string($cp) </syntaxhighlight>

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.