Building tree array of objects from flat array of objects [duplicate]

Question

I want to build a tree array from flat array:

Here is the flat array:

nodes = [
    {id: 1, pid: 0, name: "kpittu"},
    {id: 2, pid: 0, name: "news"},
    {id: 3, pid: 0, name: "menu"},
    {id: 4, pid: 3, name: "node"},
    {id: 5, pid: 4, name: "subnode"},
    {id: 6, pid: 1, name: "cace"}
];

NB: id = node id; pid = parent node id.

I want to transform it into this array:

nodes = [{
    id: 1,
    name: 'kpittu',
    childs: [{
        id: 6,
        name: 'cace'
    }]
}, {
    id: 2,
    name: 'news'
}, {
    id: 3,
    name: 'menu',
    childs: [{
        id: 4,
        name: 'node',
        childs: [{
            id: 5,
            name: 'subnode'
        }]
    }]
}];

I tried to use a recursive function to achieve the expected result, but I'm looking for a better approach. Thanks for your response.

Answer 1

You could use a hash table and take id and pid in every loop as connected nodes.

This proposal works with unsorted data as well.

var nodes = [{ id: 6, pid: 1, name: "cace" }, { id: 1, pid: 0, name: "kpittu" }, { id: 2, pid: 0, name: "news" }, { id: 3, pid: 0, name: "menu" }, { id: 4, pid: 3, name: "node" }, { id: 5, pid: 4, name: "subnode" }],
    tree = function (data, root) {
        var r = [], o = {};
        data.forEach(function (a) {
            if (o[a.id] && o[a.id].children) {
                a.children = o[a.id] && o[a.id].children;
            }
            o[a.id] = a;
            if (a.pid === root) {
                r.push(a);
            } else {
                o[a.pid] = o[a.pid] || {};
                o[a.pid].children = o[a.pid].children || [];
                o[a.pid].children.push(a);
            }
        });
        return r;
    }(nodes, 0);

console.log(tree);

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Answer 2

You can also use Map object, introduced in ES6.

let nodes = [
  { id: 1, pid: 0, name: "kpittu" },
  { id: 2, pid: 0, name: "news" },
  { id: 3, pid: 0, name: "menu" },
  { id: 4, pid: 3, name: "node" },
  { id: 5, pid: 4, name: "subnode" },
  { id: 6, pid: 1, name: "cace" }
];

function toTree(arr) {
  let arrMap = new Map(arr.map(item => [item.id, item]));
  let tree = [];

  for (let i = 0; i < arr.length; i++) {
    let item = arr[i];

    if (item.pid) {
      let parentItem = arrMap.get(item.pid);

      if (parentItem) {
        let { children } = parentItem;

        if (children) {
          parentItem.children.push(item);
        } else {
          parentItem.children = [item];
        }
      }
    } else {
      tree.push(item);
    }
  }

  return tree;
}

let tree = toTree(nodes);

console.log(tree);