Converting an array into a nested object in javascript

Question

I have typical organization hierarchy. For example.

D,E is reporting to B. B,C is reporting to A.

A is the top most node. But I receive this data as a flat array with an attribute pointing to the parent.

    [{
      name: "A",
      parent: null
    },
    {
      name: "B",
      parent: "A"
    },
    {
      name: "C",
      parent: "A"
    },
    {
      name: "D",
      parent: "B"
    },
    {
      name: "E",
      parent: "B"
    }]

But I want to convert this in to single nested object or a tree. A root node has children attribute with the children embedded and each child has its own children attribute like this.

    {
      name: "A",
      children: [{
        name: "C"
        children: [{
          name: "D"
        },{
          name: "E"
        }]
      },{
        name: "C"
      }]
    }

How can I do this in javascript efficiently?

Answer 1

Unlike the other solutions, this uses a single loop - the order of data is unimportant - example is not in the same order as question

var peeps = [
    { name: "D", parent: "B" }, 
    { name: "B", parent: "A" },
    { name: "A", parent: null }, 
    { name: "C", parent: "A" }, 
    { name: "E", parent: "B" }
];

var tree;
var obj = {};
peeps.forEach(function (peep) {
    var name = peep.name,
        parent = peep.parent,
        a = obj[name] || { name: name };
    if (parent) {
        obj[parent] = obj[parent] || { name: parent };
        obj[parent].children = obj[parent].children || [];
        obj[parent].children.push(a);
    } else {
        tree = obj[name];
    }
    obj[name] = obj[name] || a;
});
console.log(tree);

Answer 2

This solution features Jaromanda X' solution with some additions.

1. Array.prototype.reduce instead of Array.prototype.forEach, because of the need of a temporary variable and the return value.

2. The content of r[a.name].children is preserved and assigned to a.children.

3. Node a is assigned to r[a.name]. Therefore all properties of the node object remain, like prop1 ... prop5.

4. The root node is assigned to r._ for later use.

var data = [
        { name: "D", parent: "B", prop1: 'prop1' },
        { name: "B", parent: "A", prop2: 'prop2' },
        { name: "A", parent: null, prop3: 'prop3' },
        { name: "C", parent: "A", prop4: 'prop4' },
        { name: "E", parent: "B", prop5: 'prop5' }
    ],
    tree = data.reduce(function (r, a) {
        a.children = r[a.name] && r[a.name].children;
        r[a.name] = a;
        if (a.parent) {
            r[a.parent] = r[a.parent] || {};
            r[a.parent].children = r[a.parent].children || [];
            r[a.parent].children.push(a);
        } else {
            r._ = a;
        }
        return r;
    }, {})._;
document.write('<pre>' + JSON.stringify(tree, 0, 4) + '</pre>');

For more than one roots, you could use the parent of root as accessor for the children and return this array

var data = [{ name: "D", parent: "B", prop1: 'prop1' }, { name: "B", parent: "A", prop2: 'prop2' }, { name: "A", parent: null, prop3: 'prop3' }, { name: "C", parent: "A", prop4: 'prop4' }, { name: "E", parent: "B", prop5: 'prop5' }, { name: "A1", parent: null, prop3: 'prop3' }],
    tree = data.reduce(function (r, a) {
        if (r[a.name] && r[a.name].children) { // prevent empty children array
            a.children = r[a.name].children;
        }
        r[a.name] = a;
        r[a.parent] = r[a.parent] || {};
        r[a.parent].children = r[a.parent].children || [];
        r[a.parent].children.push(a);
        return r;
    }, {}).null.children; // take root value as property accessor

console.log(tree);

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Answer 3

You can do this using while loop:

var data = [
    { name: "A", parent: null },
    { name: "B", parent: "A" },
    { name: "C", parent: "A" },
    { name: "D", parent: "B" },
    { name: "E", parent: "B" }
];

var root = data.find(function(item) {
    return item.parent === null;
});

var tree = {
    name: root.name
};

var parents = [tree];
while (parents.length > 0) {
    var newParents = [];
    parents.forEach(function(parent) {
        var childs = data.filter(function(item) {
            return item.parent == parent.name
        }).forEach(function(child) {
            var c = { name: child.name };
            parent.children = parent.children || [];
            parent.children.push(c);
            newParents.push(c);
        });
    });
    parents = newParents;
}

console.log(tree);