Push object into array in recursion

Question

I have two arrays: first arr - has multiple level structure.
second arr - linear array with objects.

In my update function I iterate throw my first array childrens and if condition true, I push objects into attributes.

In production - I have arr2.length - 150000 objects and arr1.length - multiple deep levels.

How I can optimize my function to loop more quickly with a big data? Now, I wait about 5 minutes on iteration.

var arr1 = [{
    "item_id": 2,
    "item_name": "test",
    "children": [{
        "item_id": 39646,
        "item_name": "test1",
        "children": [{
            "item_id": 35648,
            "item_name": "test2",
            "children": [{
                "item_id": 35771,
                "item_name": "test3",
                "children": [],
                "attributes": []
            }],
        }]
    }]
}]


var arr2 = [
    {
        "item_id": 35771,
        "attr_value": "test",
    }, {
        "item_id": 35771,
        "attr_value": "test1",
    }
]


const update = (array, id, object) => array.forEach(o => o.item_id === id ?
    o.attributes.push(object) : update(o.children, id, object)
);

for (let item of arr2) {
   update(arr1, item.item_id, item);
}

console.log(arr1)

That use of .some() doesn't make any sense. .some() returns true when at least one of the elements of an array satisfies a given predicate. You're misusing it as a .forEach() o.O — Andreas
– Andreas, Commented Apr 14, 2022 at 8:58

Scott Sauyet · Accepted Answer · 2022-04-14 13:52:28Z

We can walk the tree once, after converting your second array into this format:

{
  35771: ['test', 'test1']
  // ...
}

and for each node of the tree just adding the attributes from this list if they exist. Here's an implementation:

const updateForest = (atts) => (forest) =>
  forest .map (({item_id, children = [], ...rest}) => ({
    item_id,
    ...rest,
    children: updateForest (atts) (children),
    ...(atts [item_id] ? {attributes: atts [item_id]} : {})
  }))

const addAttributes = (forest, atts) => 
  updateForest (atts .reduce (
    (a, {item_id, attr_value}) => ((a [item_id] = a [item_id] || []), (a [item_id] .push (attr_value)), a), 
    {}
  )) (forest)

const arr1 = [{item_id: 2, item_name: "test", children: [{item_id: 39646, item_name: "test1", children: [{item_id: 35648, item_name: "test2", children: [{item_id: 35771, item_name: "test3", children: [], attributes: []}]}]}]}]
const arr2 = [{item_id: 35771, attr_value: "test"}, {item_id: 35771, attr_value: "test1"}]


console .log (addAttributes (arr1, arr2))

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

updateForest receives the attributes reformatted as described and returns a function which takes your forest structure (it's not a tree, because it's not necessarily singly-rooted) and visits its nodes, adding attributes if they exist, recurring on the list of children.

Our public function is addAttributes. This uses reduce to do that format conversion on your attributes, passing it and then the forest to updateForest.

It's important to not that this does not mutate your original structures, but creates new ones. I find this an important goal when coding. But if your data is so large that we can't fit two copies in memory, then we'd have to skip this approach.

Andrei · Accepted Answer · 2022-04-14 09:18:43Z

One way would be to create a map that tells you exactly where to find the item in arr1.
Something like this:

const mappedArr1 = {
    2: {}, // Reference to item 2
    39646: {}, // Reference to item 39646
    35648: {}, // Reference to item 35648
    35771: {}, // Reference to item 35771
}

And when you update just do:

const item = mappedArr1[id];
item.attributes.push(object);

To create the map maybe use something like this:

const map = array => {
  const data = {};
  const doMap = array => array.forEach(i => {
    data[i.item_id] = i;
    if (i.children && i.children.length > 0) {
      doMap(i.children);
    }
  });
  doMap(array);
    return data;
}

const mappeArr1 = map(arr1);

Here is the full code:

var arr1 = [{
    "item_id": 2,
    "item_name": "test",
    "children": [{
        "item_id": 39646,
        "item_name": "test1",
        "children": [{
            "item_id": 35648,
            "item_name": "test2",
            "children": [{
                "item_id": 35771,
                "item_name": "test3",
                "children": [],
                "attributes": []
            }],
        }]
    }]
}]


var arr2 = [
    {
        "item_id": 35771,
        "attr_value": "test",
    }, {
        "item_id": 35771,
        "attr_value": "test1",
    }
]

const map = array => {
  const data = {};
  const doMap = array => array.forEach(i => {
    data[i.item_id] = i;
    if (i.children && i.children.length > 0) {
      doMap(i.children);
    }
  });
  doMap(array);
  return data;
}

const mappedArr1 = map(arr1);

for (let i of arr2) {
   const item = mappedArr1[i.item_id];
   item.attributes.push(i.attr_value);
}

console.log(arr1)

Use JSBench to test the performance of multiple implementations, you will need a bigger data sample: https://jsbench.me

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