Construct hierarchy tree from flat list with parent field?

Question

I have a list of "page" objects with a parent field. This parent field references another object in the list. I would like to create a tree hierarchy from this list based on this field.

Here is what my original list looks like:

[
  {
    id: 1,
    title: 'home',
    parent: null
  },
  {
    id: 2,
    title: 'about',
    parent: null
  },
  {
    id: 3,
    title: 'team',
    parent: 2
  },
  {
    id: 4,
    title: 'company',
    parent: 2
  }
]

I would like to convert it into a tree structure like this:

[
  {
    id: 1,
    title: 'home',
    parent: null
  },
  {
    id: 2,
    title: 'about',
    parent: null,
    children:  [
      {
        id: 3,
        title: 'team',
        parent: 2
      },
      {
        id: 4,
        title: 'company',
        parent: 2
      }
    ]
]

I was hoping for a reusable function that I can call against an arbitrary list any time. Anyone know of a good way to handle this? Any help or advice would be greatly appreciated!

Answer 1

function treeify(list, idAttr, parentAttr, childrenAttr) {
    if (!idAttr) idAttr = 'id';
    if (!parentAttr) parentAttr = 'parent';
    if (!childrenAttr) childrenAttr = 'children';

    var treeList = [];
    var lookup = {};
    list.forEach(function(obj) {
        lookup[obj[idAttr]] = obj;
        obj[childrenAttr] = [];
    });
    list.forEach(function(obj) {
        if (obj[parentAttr] != null) {
            if (lookup[obj[parentAttr]] !== undefined) {
                lookup[obj[parentAttr]][childrenAttr].push(obj);
            } else {
                 //console.log('Missing Parent Data: ' + obj[parentAttr]);
                 treeList.push(obj);
            }               
        } else {
            treeList.push(obj);
        }
    });
    return treeList;
};

Fiddle