JavaScript: Convert linear JSON array into tree structure with unknown depth

Question

I have a JavaScript array like this:

[{ 
   name:'a'
   level:1
 },{ 
   name:'b'
   level:2
 },{
   name:'c'
   level:3
 },{ 
   name:'d'
   level:2
 },{ 
   name:'e'
   level:1
 },{ 
   name:'f'
   level:2
 },{ 
   name:'g'
   level:2
 },{
   name: 'f',
   level: 1
 }
]

I need this to be converted into a tree structure based on level property of objects

[{
    name: 'a'
    level: 1
    children: [{
        name: 'b'
        level: 2,
        children: [{
            name: 'c',
            level: 3
        }]
    }, {
        name: 'd'
        level: 2
    }]
}, {
    name: 'e'
    level: 1,
    children: [{
        name: 'f'
        level: 2
    }, {
        name: 'g'
        level: 2
    }]
}, {
    name: 'f',
    level: 1
}]

I have tried writing many functions and tried many approaches but failed. One thing I realized is that this can be achieved only by writing a recursive function. Please help.

NOTE: the level depth is not limited to 3, it is unknown

Answer 1

Here is a quick go at it:

var res = convert(a);

console.log(res);

function convert(arr) {
    return treeify(splitToSegments(arr));
}

function splitToSegments(arr) {
    var ret = [];
    var accum, segment;

    arr.forEach(function(o) {
        if (o.level === 1) {
            accum = true;

            if (segment && segment.length) {
                ret.push(segment);
            }

            segment = [o];
        } else if (accum) {
            segment.push(o);
        }
    });

    if (segment && segment.length) {
        ret.push(segment);
    }

    return ret;
}

function treeify(arr) {
    return arr.map(function(o) {
        return o.reduce(function(a, b) {
            var lastChild;

            a.children = a.children || [];

            if (a.level + 1 === b.level) {
                a.children.push(b);
            } else {
                lastChild = a.children[a.children.length - 1];

                lastChild.children = lastChild.children || [];

                lastChild.children.push(b);
            }

            return a;
        });
    });
}

Note that treeify might need some extra logic to deal with the siblings but it should be an okish starting point.