The saxon:tabulate-maps instruction selects a collection of maps and expands them by adding information from containing maps and arrays in a hierarchic structure (typically obtained by parsing JSON). The result is an array of maps which can be considered as a table with one row for each leaf in the tree, with data from upper levels of the hierarchy replicated in each relevant row of the table.

Category: instruction
Content: none
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element




XPath expression selecting the root of a tree of maps and arrays



XPath expression selecting a sequence of maps relative to the root of the tree


The effect of the instruction is easiest to illustrate by example. Consider the structure that results from parsing the JSON input:

[{ "country": "UK", "cities: [ { "name": "London", "population" : 7200000 }, { "name": "Birmingham", "population": 992000 }, { "name": "Leeds", "population": 720000 } ]}, { "country": "France" "cities": [ { "name": "Paris", "population" : 12341418 }, { "name": "Lyon", "population": 2214068 }, { "name": "Marseille", "population": 1727070 } ]} ]

This can be processed using the instruction:

<saxon:tabulate-maps root="parse-json($input)" select="?*?cities?*"/>

which delivers the result (serialized as JSON, with whitespace added for clarity):

[{"name":"London", "population":7.2E6, "_keys":[1,"cities",1], "country":"UK"}, {"name":"Birmingham", "population":992000, "_keys":[1,"cities",2], "country":"UK"}, {"name":"Leeds", "population":720000, "_keys":[1,"cities",3], "country":"UK"}, {"name":"Paris", "population":1.2341418E7, "_keys":[2,"cities",1], "country":"France"}, {"name":"Lyon", "population":2.214068E6, "_keys":[2,"cities",2], "country":"France"}, {"name":"Marseille", "population":1.72707E6, "_keys":[2,"cities",3], "country":"France"}]

The result is thus an array of maps, corresponding one-to-one with the maps selected in the select expression, with each map in the output containing:

  1. Copies of the entries (key-value pairs) in the original map
  2. Copies of all entries in containing maps, other than the containing entry
  3. A new entry, _keys, containing an array of map keys and array indexes representing a path from the root to the selected map.

If the added entries have key values that would conflict with existing entries, the key is modified by the addition of a numeric suffix.

The effect of the instruction is thus to create a flat structure (an array of maps) in which data from upper levels of the hierarchic structure is duplicated in each row of the result.