How to make directory structure from array of JSON objects

Question

I have an JSONArray(org.json.JSONArray) of JSONObjects(org.json.JSONObject) like

[
    {"id":"abc", "parent_id":""},
    {"id":"def", "parent_id":"abc"},
    {"id":"ghi", "parent_id":""},
    {"id":"jkl", "parent_id":"abc"},
    {"id":"mno", "parent_id":"ghi"},
    {"id":"mno", "parent_id":"def"},
]

Here "id" field represents unique id of the Object and "parent_id" represents id of it's parent. I have to convert this JSONArray into another JSONArray where I can have elements nested inside their parent(directory like structure) like

[
    {"id":"abc", "parent_id":"","children":[
        {"id":"def", "parent_id":"abc","children":[
            {"id":"mno", "parent_id":"def","children":[]}
        ]},
        {"id":"jkl", "parent_id":"abc","children":[]}
    ]},
    {"id":"ghi", "parent_id":"","children":[
        {"id":"mno", "parent_id":"ghi","children":[]}
    ]},
]

Can anybody help me here what is the best possible way to do so?

anthony sottile · Accepted Answer · 2013-03-12 14:26:27Z

2

You'll have something like this (pseudo code)

// Element is { id, children }
Dictionary<String, Element> elements;

for (JSONObject obj : arr) {
    if (elements.hasKey(obj.id)) {
        // Maybe you need to update your element or something here
    } else {
        // Create your element
        elements[obj.id] = new Element(obj.id);
    }

    // if the parent does not exist, create a shadow of the parent
    // (it'll get filled in with more info above if encountered later)
    if (!elements.hasKey(obj.parent)) {
        elements[obj.parent] = new Element(obj.parent);
    }

    // Add yourself to children
    elements[obj.parent].children.push(elements[obj.id]);
}

// TODO: iterate your dictionary and put it into an array, this should be straightforward
// Or if you want the root of your tree return elements[""]

I apologize in advance for not being more specific, but this should work pretty generically for whatever you want to do. Also it's not Java, but easily convertible.

answered Mar 12, 2013 at 14:26

anthony sottile

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5 Comments

rahul0789 Over a year ago

Thank you Anthony but your answer will work only if there is one level (parent>children) inside the hierarchy. The children may be nested up to n levels (parent>children>grand children and so on...).

anthony sottile Over a year ago

This should work approximately as posted. elements[""] should contain the root, which will have children that point at the other elements inside elements. I'll have to check my c# implementation of this when I get home (I needed to do the exact same thing except mine was folding a tree from a database)

anthony sottile Over a year ago

@rahul0789: Since I don't have a way of showing it in java, here's a javascript proof of concept: jsfiddle.net/Ngd9H/1

H Raval Over a year ago

this code only provides two level...what if i want n level of parent-child

anthony sottile Over a year ago

You'll have to clarify, as written this works for however nested you want.

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