Recursive function to flatten nested array and keeping track of all parent nodes (Javascript)

Question

Hi I have a function that takes nested array of parents containing children and flatten it. However, I would like to also keep track of all of its higher nodes ids.

Example data structure:

[{
    id: 1,
    type: "group",
    name: "Colors",
    items: [
      { id: 2, type: "item", name: "Red", items: [] },
      { id: 3, type: "item", name: "Purple2", items: [] },
      {
        id: 4,
        type: "item",
        name: "Black",
        items: [
          {
            id: 5,
            type: "item",
            name: "Purple3",
            items: [],
          },
          { id: 6, type: "item", name: "Purple4", items: [] },
        ],
      },
    ],
  }]

This is current end result (this is exactly what I want to achieve), but potentially functions below can be refactored.

{id: 1, name: "Colors", depth: 1, parentId: null, main: []}
1: {id: 2, name: "Red", depth: 2, parentId: 1, main: [1]}
2: {id: 3, name: "Purple2", depth: 2, parentId: 1, main: [1]}
3: {id: 4, name: "Black", depth: 2, parentId: 1, main: [1]}
4: {id: 5, name: "Purple3", depth: 3, parentId: 4, main: [1,4]} // main stores id of all higher parents e.g. id 4 = "black" and parent of 4 = "Colors"
5: {id: 6, name: "Purple4", depth: 3, parentId: 4, main: [1,4]}

My current flatten array function:

const flattenArr = (data, depth = 1, parent = null) => {
  const result = [];

  data.forEach((item) => {
    const { id, name, items } = item;
    result.push({
      id,
      name,
      depth,
      parentId: parent,
      main: [],
    });

    if (items) result.push(...flattenArr(items, depth + 1, item.id));
  });

  return result;
};

The function below is used to keep track of all parent ids. However it does not seem to be most optimal solution that I can use therefore I would like to know whether it can be improved possibly to be done all in one recursive function.

const collectParents = (arr) => {
  for (let b = 0; b < arr.length; b++) {
    if (arr[b].depth !== 1) {
      arr[b].main.push(
        ...arr[b - 1].main,
        arr[b - 1].depth === arr[b].depth - 1 ? arr[b - 1].id : null
      );
    }
  }

  arr.forEach((x) => (x.main = x.main.filter((i) => i !== null)));
};

Answer 1

You couldt take Array#flatMap with a closure over main and depth .

 const flat = (main = [], depth = 1,) => ({ top, type, items = [], ...o }) => [ { ...o, depth, parentId: main[0] ?? null, main }, ...items.flatMap(flat([...main, o.id], depth + 1)) ], tree = [{ id: 1, type: "group", name: "Colors", items: [{ id: 2, type: "item", name: "Red", items: [], top: new Set() }, { id: 3, type: "item", name: "Purple2", items: [] }, { id: 4, type: "item", name: "Black", items: [{ id: 5, type: "item", name: "Purple3", items: [] }, { id: 6, type: "item", name: "Purple4", items: [] }] }] }], result = tree.flatMap(flat()); console.log(result);

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

Answer 2

You could create recursive function using reduce method and pass down parent id and an array of previous ids.

 const data = [{"id":1,"type":"group","name":"Colors","items":[{"id":2,"type":"item","name":"Red","items":[],"top":{}},{"id":3,"type":"item","name":"Purple2","items":[]},{"id":4,"type":"item","name":"Black","items":[{"id":5,"type":"item","name":"Purple3","items":[]},{"id":6,"type":"item","name":"Purple4","items":[]}]}]}] function flatten(data, depth = 0, parentId = null, main = []) { return data.reduce((r, { items, id, ...rest }) => { const obj = { ...rest, id, depth, parentId, main } r.push(obj) if (items.length) { r.push(...flatten(items, depth + 1, id, [...main, id])) } return r; }, []) } const result = flatten(data) console.log(result)