Sorting Nested JSON Objects

JSON Objects can contain an arbitrary number of keys and values (for which the value may itself be another JSON object). For example, a nested JSON object called "Monsters" might look like this:

{
 "Troll":
  {
    "name":"Troll",
    "HD":4,
    "HP":75
  },
 "Orc":
  {
    "name":"Orc",
    "HD":3,
    "HP":22
  }
}

Note that each value in the key-value pairs in the above object is actually a complete JSON object in its own right.

It is occasionally useful to be able to sort a JSON object that contains other JSON objects based on a value in one of the "sub-objects." For instance, if a JSON object exists that contains token names and distances to those tokens from a given point, one may want to sort the JSON so that the nearest objects are first, and the farthest are last.

Or, using the above "Monsters" example, one may wish to sort it by name, or by HP, or by HD.

The following macro routine is a generic method to sort JSON objects based on an arbitrary value within a nested object.

Assumptions

• This macro requires the use of a JSON object supporting version of MapTool; it was written and tested in version 1.3.b53.
• The macro is generic, and will run using any given JSON object conforming to the general "nested object" structure. In this case, a nested JSON object is created in the beginning so that there is a sample object to sort. However: this routine should be applicable to JSON arrays of objects as well - it would simply require using the index of the nested object rather than the nested object's key.
• It can be unclear which object is being discussed when you have multiply nested objects. In the following explanation, "nested object" will always refer to an object contained within a larger JSON. So, the larger object is Monsters, while Troll would be a nested object.

Macro Code and Discussion

Please see the full macro code for the complete macro.

Create Sample Object

This sequence simply creates a sample object to practice sorting. In actual use, you may wish to pass an object as an argument, or pull an object from a token's properties, as necessary.

[h:troll = json.set("{}", "name", "Troll", "HD", 4, "HP", 75)]
[h:orc = json.set("{}", "name", "Orc", "HD", 3, "HP", 13)]
[h:goblin = json.set("{}", "name", "Goblin", "HD", 2, "HP", 6)]
[h:gnoll = json.set("{}", "name", "Gnoll", "HD", 3, "HP", 19)]
[h:kobold=json.set("{}", "name", "Kobold", "HD", 1, "HP", 4)]
[h:monsters = json.set("{}", "Troll", troll, "Orc", orc, "Goblin", goblin, "Gnoll", gnoll, "Kobold", kobold)]

Request Sorting Key and Sort Direction from User

This section is also optional (and not useful if this macro will be used as a function/called macro), but for the example code it makes it easier to experiment with. This section uses input() to gather user input, and abort() to halt processing if the user hits "Cancel." Finally, it uses an IF(): roll option to set a variable with a "friendly" indicator of sort direction, which will be used at the end in the final output.

[h:status = input(
"whichKey|name,HD,HP|Pick Sorting Key|LIST|SELECT=0 VALUE=STRING",
"whichDirection|A+,A-,N+,N-|Direction (A+/- for strings, N+/- for numbers!)|LIST|SELECT=0 VALUE=STRING"
)]
[h:abort(status)]

[h,if(substring(whichDirection,1)=="+"): dirString = "ascending"; dirString = "descending"]

Set Basic Variables

This segment initializes some variables that will be used later:

• sortObj is the object to be sorted
• sortOn is the value on which to sort
• sortDirection is the direction of the sort, which will be passed to listSort()
• sortObjContentList is a list - created using json.fields() - of each key in the object to be sorted; effectively it is a list of the "names" of each item in the JSON object we wish to sort
• keyList is a list containing the values of sortKey drawn from each nested object within sortObj
• sortedJSON will hold the sorted JSON object; the original object will be unchanged.

[h:sortObj=monsters]
[h:sortKey = whichKey]
[h:sortDirection = whichDirection]
[h:sortObjContentList = json.fields(sortObj)]
[h:keyList = ""] 
[h:sortedJSON = "{}"]

Extract the Value of sortKey from each Nested Object

Here, we iterate over sortObjContentList, and use the value of each element in the list - assigned to the variable item - to extract the nested objects from the larger Monsters object.

With the nested objects extracted, we can then retrieve the value of the sorting key by using json.get(). That value is appended to the previously empty list keyList. Finally, once each nested object's value for sortKey has been extracted and added to keyList, keyList is sorted using listSort() based on the direction specified by the user.

[h,foreach(item, sortObjContentList),CODE:
{
   [h:itemDetail = json.get(sortObj,item)]
   [h: keyList = listAppend(keyList, json.get(itemDetail, sortKey))]
}]

[h:keyList = listSort(keyList, sortDirection)]

Iterating through keyList and Each Nested Object

This is the most complex part of the routine. Here, we use FOREACH(): to iterate over the contents of keyList (which, you will recall, contains the values corresponding to sortKey for each nested object). For each element in keyList, we then iterate through all of the nested objects in Monsters to see which one(s) match up to the current element of keyList.

So, for example, if the current value - key - in the outer loop is 4, and we are sorting by "HD", the inner loop will iterate through each nested object and check to see if the value of "HD" for that nested object is equal to 4.

If a match is found, the matching nested object is added to sortedJSON using json.set(). In this fashion, the two loops will combine to build a new JSON Object (sortedJSON) whose nested objects are in the requested order.

[h,foreach(key,keyList),CODE:
{
   [foreach(object,sortObj),CODE:
   {
     [objectDetail = json.get(sortObj,object)]
     [h:sortOnValue = json.get(objectDetail, sortKey)]
     [if(sortOnValue == key): sortedJSON=json.set(sortedJSON, object, objectDetail);""]
   }]
}]

Outputting the Results in an Attractive Fashion

The final step is to output results. The use of json.indent() here simply makes the sorted JSON object easy to read.

JSON Object sorted by [r:whichKey], [r:dirString]:<br>
<pre>[r:json.indent(sortedJSON, 3)]</pre>