Map Module

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This XQuery Module contains functions for manipulating maps, which will officially be introduced with XQuery 3.1.
Please note that the functions are subject to change until the specification has reached its final stage.


All functions in this module are assigned to the namespace, which is statically bound to the map prefix.


Some examples use the map $week defined as:

declare variable $week as map(*) := map {
  0: "Sonntag",
  1: "Montag",
  2: "Dienstag",
  3: "Mittwoch",
  4: "Donnerstag",
  5: "Freitag",
  6: "Samstag"


Signatures map:contains($input as map(*), $key as xs:anyAtomicType) as xs:boolean
Summary Returns true if the map supplied as $input contains an entry with a key equal to the supplied value of $key; otherwise it returns false. No error is raised if the map contains keys that are not comparable with the supplied $key.

If the supplied key is xs:untypedAtomic, it is compared as an instance of xs:string. If the supplied key is the xs:float or xs:double value NaN, the function returns true if there is an entry whose key is NaN, or false otherwise.

  • map:contains($week, 2) returns true().
  • map:contains($week, 9) returns false().
  • map:contains(map {}, "xyz") returns false().
  • map:contains(map { "xyz": 23 }, "xyz") returns true().


Signatures map:entry($key as xs:anyAtomicType, $value as item()*) as map(*)
Summary Creates a new map containing a single entry. The key of the entry in the new map is $key, and its associated value is $value.

The function map:entry is intended primarily for use in conjunction with the function map:merge. For example, a map containing seven entries may be constructed like this:

  map:entry("Su", "Sunday"),
  map:entry("Mo", "Monday"),
  map:entry("Tu", "Tuesday"),
  map:entry("We", "Wednesday"),
  map:entry("Th", "Thursday"),
  map:entry("Fr", "Friday"),
  map:entry("Sa", "Saturday")

Unlike the map { ... } expression, this technique can be used to construct a map with a variable number of entries, for example:

map:merge(for $b in //book return map:entry($b/isbn, $b))
Examples map:entry("M", "Monday") creates map { "M": "Monday" }.


Signatures map:for-each($input as map(*), $fun as function(xs:anyAtomicType, item()*) as item()*) as item()*
Summary Applies a function to every entry of the map $input and returns the results as a sequence. The function supplied as $fun takes two arguments. It is called supplying the key of the map entry as the first argument, and the associated value as the second argument.
Examples The following query adds the keys and values of all map entries and returns (3,7):
  map { 1: 2, 3: 4 },
  function($a, $b) { $a + $b }


Signatures map:get($input as map(*), $key as xs:anyAtomicType) as item()*
Summary Returns the value associated with a supplied key in a given map. This function attempts to find an entry within the map supplied as $input that has a key equal to the supplied value of $key. If there is such an entry, the function returns the associated value; otherwise it returns an empty sequence. No error is raised if the map contains keys that are not comparable with the supplied $key. If the supplied key is xs:untypedAtomic, it is converted to xs:string.

A return value of () from map:get could indicate that the key is present in the map with an associated value of (), or it could indicate that the key is not present in the map. The two cases can be distinguished by calling map:contains. Invoking the map as a function item has the same effect as calling get: that is, when $input is a map, the expression $input($K) is equivalent to get($input, $K). Similarly, the expression get(get(get($input, 'employee'), 'name'), 'first') can be written as $input('employee')('name')('first').

  • map:get($week, 4) returns "Donnerstag".
  • map:get($week, 9) returns (). (When the key is not present, the function returns an empty sequence.).
  • map:get(map:entry(7,())), 7) returns (). (An empty sequence as the result can also signify that the key is present and the associated value is an empty sequence.).


Signatures map:keys($input as map(*)) as xs:anyAtomicType*
Summary Returns a sequence containing all the key values present in a map. The function takes any map as its $input argument and returns the keys that are present in the map as a sequence of atomic values. The order may differ from the order in which entries were inserted in the map.
  • map:keys(map { 1: "yes", 2: "no" }) returns (1,2).


Signatures map:merge($input as map(*)*) as map(*)
Summary Constructs and returns a new map. The map is formed by combining the contents of the maps supplied in the $input argument. The maps are combined as follows:
  1. There is one entry in the new map for each distinct key value present in the union of the input maps, where keys are considered distinct according to the rules of the distinct-values function.
  2. The associated value for each such key is taken from the last map in the input sequence $input that contains an entry with this key.

There is no requirement that the supplied input maps should have the same or compatible types. The type of a map (for example map(xs:integer, xs:string)) is descriptive of the entries it currently contains, but is not a constraint on how the map may be combined with other maps.

  • map:merge(()) creates an empty map.
  • map:merge((map:entry(0, "no"), map:entry(1, "yes"))) creates map { 0: "no", 1: "yes" }.
  • map:merge(($week, map { 7: "Unbekannt" })) creates map { 0: "Sonntag", 1: "Montag", 2: "Dienstag", 3: "Mittwoch", 4: "Donnerstag", 5: "Freitag", 6: "Samstag", 7: "Unbekannt" }.
  • map:merge(($week, map { 6: "Sonnabend" })) creates map { 0: "Sonntag", 1: "Montag", 2: "Dienstag", 3: "Mittwoch", 4: "Donnerstag", 5: "Freitag", 6: "Sonnabend" }.


Signatures map:put($input as map(*), $key as xs:anyAtomicType, $value as item()*) as map(*)
Summary Creates a new map, containing the entries of the $input argument and a new entry composed by $key and $value. The semantics of this function are equivalent to map:merge(($input, map { $key, $value }))


Signatures map:remove($input as map(*), $key as xs:anyAtomicType) as map(*)
Summary Constructs a new map by removing an entry from an existing map. The entries in the new map correspond to the entries of $input, excluding any entry whose key is equal to $key.

No failure occurs if the input map contains no entry with the supplied key; the input map is returned unchanged

  • map:remove($week, 4) creates map { 0: "Sonntag", 1: "Montag", 2: "Dienstag", 3: "Mittwoch", 5: "Freitag", 6: "Samstag" }.
  • map:remove($week, 23) creates map { 0: "Sonntag", 1: "Montag", 2: "Dienstag", 3: "Mittwoch", 4: "Donnerstag", 5: "Freitag", 6: "Samstag" }.


Signatures map:size($input as map(*)) as xs:integer
Summary Returns a the number of entries in the supplied map. The function takes any map as its $input argument and returns the number of entries that are present in the map.
  • map:size(map:merge(())) returns 0.
  • map:size(map { "true": 1, "false": 0 }) returns 2.


Signatures map:serialize($input as map(*)) as xs:string
Summary This function is specific to BaseX. It returns a string representation of the supplied map. The purpose of this function is to get an insight into the structure of a map item; it cannot necessarily be used for reconstructing the original map.
  • map:serialize(map { 'A': (.1, xs:date('2001-01-01')) }) returns { "A": (0.1, "2001-01-01") }.


Version 8.0
  • Added: map:for-each, map:merge, map:put
  • Removed: support for collations (in accordance with the XQuery 3.1 spec).
  • Removed: map:new (replaced with map:merge)
  • Updated: aligned with latest specification: compare keys of type xs:untypedAtomic as xs:string instances, store xs:float or xs:double value NaN.
  • Introduction on maps is now found in the article on XQuery 3.1.
Version 7.8
Version 7.7.1
  • Updated: alternative map syntax without map keyword and : as key/value delimiter (e.g.: { 'key': 'value' })