B4J Question How to Unflatten List to a JSON Tree?

[Mashiane]

Hi there

Can anyone please help with a snippet to unflatten data into a json stree?

For example, this is my list of records...

Dim arr As List
arr.Initialize
arr.Add(CreateMap("id":1 ,"parentid" : 0))
arr.Add(CreateMap("id":4 ,"parentid" : 2))
arr.Add(CreateMap("id":3 ,"parentid" : 1))
arr.Add(CreateMap("id":5 ,"parentid" : 0))
arr.Add(CreateMap("id":6 ,"parentid" : 0))
arr.Add(CreateMap("id":2 ,"parentid" : 1))
arr.Add(CreateMap("id":7 ,"parentid" : 4))
arr.Add(CreateMap("id":8 ,"parentid" : 1))

To something like...

[
 {
  "id": 1,
  "parentid": 0,
  "children": [
   {
    "id": 2,
    "parentid": 1,
    "children": [
     {
      "id": 4,
      "parentid": 2,
      "children": [
       {
        "id": 7,
        "parentid": 4,
        "children": []
....
....
       }

 

[Brandsum]

Code:

Dim arr As List
arr.Initialize
arr.Add(CreateMap("id":1 ,"parentid" : 0, "children": Null))
arr.Add(CreateMap("id":4 ,"parentid" : 2, "children": Null))
arr.Add(CreateMap("id":3 ,"parentid" : 1, "children": Null))
arr.Add(CreateMap("id":5 ,"parentid" : 0, "children": Null))
arr.Add(CreateMap("id":6 ,"parentid" : 0, "children": Null))
arr.Add(CreateMap("id":2 ,"parentid" : 1, "children": Null))
arr.Add(CreateMap("id":7 ,"parentid" : 4, "children": Null))
arr.Add(CreateMap("id":8 ,"parentid" : 1, "children": Null))

For Each m As Map In arr
    For Each mm As Map In arr
        If m.get("id") = mm.Get("parentid") Then
            Dim l As List
            If m.Get("children") = Null Then
                l.Initialize
            Else
                l = m.Get("children")
            End If
            l.Add(mm)
           
            m.put("children",l)
        End If
    Next
Next
Dim finalArr As List:finalArr.Initialize
For Each m As Map In arr
    If m.Get("parentid") = 0 Then finalArr.Add(m)
Next
   
Dim json As JSONGenerator
json.Initialize2(finalArr)
Log(json.ToPrettyString(4))

Output:

[
    {
        "id": 1,
        "parentid": 0,
        "children": [
            {
                "id": 3,
                "parentid": 1,
                "children": null
            },
            {
                "id": 2,
                "parentid": 1,
                "children": [
                    {
                        "id": 4,
                        "parentid": 2,
                        "children": [
                            {
                                "id": 7,
                                "parentid": 4,
                                "children": null
                            }
                        ]
                    }
                ]
            },
            {
                "id": 8,
                "parentid": 1,
                "children": null
            }
        ]
    },
    {
        "id": 5,
        "parentid": 0,
        "children": null
    },
    {
        "id": 6,
        "parentid": 0,
        "children": null
    }
]

 

[Mashiane]

@Brandsum Thanks a mill. Managed to follow your logic and rewrote the main script so that I add the 'children' internally within the script

'unflatten as list of map objects using id, parentid, data attributes
Sub Unflatten(data As List) As List
    'id, parentid, data
    Dim tree As List
    Dim mappedArr As Map
    '
    tree.Initialize
    mappedArr.Initialize
    '
    'create a temp map to hold everything with 'children' as 'data'
    For Each arrElem As Map In data
        Dim dID As String = arrElem.Get("id")
        '
        Dim children As List
        children.Initialize
        arrElem.Put("data", children)
        '
        mappedArr.Put(dID, arrElem)
    Next
    '
    For Each dID As String In mappedArr.Keys
        Dim mappedElem As Map = mappedArr.Get(dID)
        Dim parentid As String = mappedElem.Get("parentid")
        ' If the element is at the root level, add it to first level elements list.
        If parentid = "" Then
            tree.Add(mappedElem)
        Else
            'If the element is not at the root level, add it to its parent list of children.
            Dim parentElem As Map = mappedArr.Get(parentid)
            Dim children As List = parentElem.Get("data")
            children.Add(mappedElem)
            parentElem.Put("data", children)
            mappedArr.Put(parentid, parentElem)
        End If
    Next
    Return tree
End Sub

 

[ThRuST]

@Mashiane You might want to create an editor for this and share? json usually calls for a simplicity in sight-reading

 

[Mashiane]

@ThRuST that wouldn’t be an overkill? I needed this for my webix explorations for three of their tree based components to be able to feed data.

So it’s a tree map to json conversion and there is already a json parser here in b4x.

If perhaps my plate wasn’t full. I want to finish my html games stuff, and also side projects I’m working on.