Using JavaScript arrow function iterate an array and create array inside array based on conditions?

Question

I have an array like the below.

 [{
  id: 1,
  is_child_question: false,
  parent_question_id: null },
{
  id: 2,
  is_child_question: true,
  parent_question_id: 1},
{
  id: 3,
  is_child_question: true,
  parent_question_id: 2}]

I want to iterate it and create a new array like below.

[{
  id: 1,
  is_child_question: false,
  parent_question_id: null,
  children: [{
    id: 2,
    is_child_question: true,
    parent_question_id: 1,
    children:[{
      id: 3,
      is_child_question: true,
      parent_question_id: 2,
      }]
  }] 
}]

Like a tree. While iterating if the node has is_child_question === true it should go under its parent node.

Answer 1

You could take a single loop approach with an object for collecting objects with id as key.

var data = [{ id: 3, is_child_question: true, parent_question_id: 2 }, { id: 2, is_child_question: true, parent_question_id: 1 }, { id: 1, is_child_question: false, parent_question_id: null }],
    tree = data.reduce((r, o) => {
        o.children = r[o.id] && r[o.id].children;
        r[o.id] = o;
        r[o.parent_question_id] = r[o.parent_question_id] || {};
        r[o.parent_question_id].children = r[o.parent_question_id].children || [];
        r[o.parent_question_id].children.push(o);
        return r;
    }, {}).null.children;

console.log(tree);

.as-console-wrapper { max-height: 100% !important; top: 0; }