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Javascript – I'm unable to create a recursion to build a tree based on a flat array

const arr = [
  {
    id: 1,
    name: 'teste',
  },

  {
    id: 2,
    name: 'teste',
    dependsOn: 1,
  },
  {
    id: 3,
    name: 'teste',
    dependsOn: 1,
  },
  {
    id: 4,
    name: 'teste',
  },
  { id: 5, name: 'dasdas', dependsOn: 2 },
]

const treeTo = [
  {
    id: 1,
    name: 'teste',
    children: [
      {
        id: 2,
        name: 'teste',
        children: [],
      },
      {
        id: 3,
        name: 'teste',
        children: [
          {
            id: 5,
            name: 'teste',
            children: [],
          },
        ],
      },
    ],
  },
  {
    id: 4,
    name: 'teste',
  },
]

I need a function to generate the tree below based on the array

function buildTree(arr, parentId = null) {
  return arr
    .filter((item) => item.dependsOn === parentId)
    .map((item) => ({
      ...item,
      children: buildTree(arr, item.id),
    }))
}

i’ve tried something like that, but I’m not that good in recursions

Tags:

2

Answers


  1. 0

    You don’t need recursion here, just make a map of the items by id and add children to appropriate parents.

    That will give you O(n) instead of O(n^2) time complexity.

    const arr=[{id:1,name:"teste"},{id:2,name:"teste",dependsOn:1},{id:3,name:"teste",dependsOn:1},{id:4,name:"teste"},{id:5,name:"dasdas",dependsOn:2},];

const nodes = arr.reduce((r, {dependsOn, ...item}) => (item.children = [], r[item.id] = item, r), {});
const result = arr.reduce((r, {dependsOn: pid, id}) => ((pid ? nodes[pid].children : r).push(nodes[id]), r), []);
console.log(result);
    .as-console-wrapper{min-height:100%!important}
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  2. 0

    If you want to keep your existing function you could also just change your filter condition to include all root level items.

    function buildTree(arr, parentId = null) {
  return arr
    .filter(item => item.dependsOn === parentId || (parentId === null && item.dependsOn === undefined))
    .map(item => ({
      ...item,
      children: buildTree(arr, item.id)
    }));
}

const arr = [
  { id: 1, name: 'teste' },
  { id: 2, name: 'teste', dependsOn: 1 },
  { id: 3, name: 'teste', dependsOn: 1 },
  { id: 4, name: 'teste' },
  { id: 5, name: 'dasdas', dependsOn: 2 }
];

const treeTo = buildTree(arr, null);
console.log(treeTo);
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