javascript recalculate deeply nested array elemnts numbers

Question

I got the following array:

let data =  [
        {"title": {number: 1},
            "children": [
                {"title": {number: 1.1}},
                {"title": {number: 1.2}},
                {"title": {number: 1.3}},
                {"title": {number: 1.4}},
                {"title": {number: 1.5}}
            ]
        },
        {"title": {number: 2},
            "children": [
                {"title":{number: 2.1}},
                {"title":{number: 2.2},
                    "children": [
                        {"title":{number: 2.2.1}},
                        {"title":{number: 2.2.2}},
                        {"title":{number: 2.2.3}},
                        {"title":{number: 2.2.4}} 
                    ]
                },
                {"title":{number: 2.3}},
                {"title":{number: 2.4}}
            ]
        },
        {"title": {number: 3},
            "children": []
        }
    ];

Every element of this array may change its place, new element may be added, existing element may be removed. The task is to recalculate elements numbers in order to maintain their correct order. For example, if element with number 2.2.2 is removed, the other elements become 2.2.1, 2.2.2 and 2.2.3. If some element is removed with its children, numbers for all other elements shoud also be recalculated. Any ideas how to do that would be welcome. Thank you

Why have numbers at all.They are easily calculated from the hierarchy — mplungjan
– mplungjan, Commented Apr 2, 2020 at 10:03
Any ideas how to find them out from hierarchy? As far as I understand I need to recursively keep track of nesting level and add increment for relevant element... — Masha
– Masha, Commented Apr 2, 2020 at 10:07
stackoverflow.com/questions/39887381/… have you checked this ? — sylvann
– sylvann, Commented Apr 2, 2020 at 10:07
Yes, you need to recurse. but as you see data[0].title is the first title, data[1]title the second. data[1].children[0] is 2.1 etc — mplungjan
– mplungjan, Commented Apr 2, 2020 at 10:11

Nenad Vracar · Accepted Answer · 2020-04-02 10:23:09Z

You could create recursive function that you will call every time your object structure changes to recalculate the positions of each element in the tree.

function recalc(data, prev = '') {
  data.forEach((e, i) => {
    let dot = prev ? '.' : '';
    let number = prev + dot + (i + 1);

    if (e.children) {
      recalc(e.children, number)
    }

    if (e.title) {
      e.title.number = number
    }
  })
}

const data1 = [{"title":{"number":1},"children":[{"title":{"number":1.1}},{"title":{"number":1.2}},{"title":{"number":1.3}},{"title":{"number":1.4}},{"title":{"number":1.5}}]},{"title":{"number":2},"children":[{"title":{"number":2.1}},{"title":{"number":2.2},"children":[{"title":{"number":"2.2.1"}},{"title":{"number":"2.2.2"}},{"title":{"number":"2.2.3"}},{"title":{"number":"2.2.4"}}]},{"title":{"number":2.3}},{"title":{"number":2.4}}]},{"title":{"number":3},"children":[]}]
recalc(data1);
console.log(data1)

const data2 = [{"title":{"number":1},"children":[{"title":{"number":1.1}},{"title":{"number":1.2}},{"title":{"number":1.5}}]},{"title":{"number":2},"children":[{"title":{"number":2.1}},{"title":{"number":2.2},"children":[{"title":{"number":"2.2.3"}},{"title":{"number":"2.2.4"}}]},{"title":{"number":2.3}},{"title":{"number":2.4}}]},{"title":{"number":3},"children":[{title: {}, children: [{title: {}}, {title: {}}]}]}]
recalc(data2);
console.log(data2)

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