Create a nested array recursively in Node.js

Question

Following is my array

[
    {id: 1, title: 'hello', parent: {number:0}},
    {id: 2, title: 'hello', parent: {number:0}},
    {id: 3, title: 'hello', parent: {number:1}},
    {id: 4, title: 'hello', parent: {number:3}},
    {id: 5, title: 'hello', parent: {number:4}},
    {id: 6, title: 'hello', parent: {number:4}},
    {id: 7, title: 'hello', parent: {number:3}},
    {id: 8, title: 'hello', parent: {number:2}}
]

and I want to have objects nested like this as output :

[
    {id: 1, title: 'hello', parent: 0, children: [
        {id: 3, title: 'hello', parent: 1, children: [
            {id: 4, title: 'hello', parent: 3, children: [
                {id: 5, title: 'hello', parent: 4},
                {id: 6, title: 'hello', parent: 4}
            ]},
            {id: 7, title: 'hello', parent: 3}
        ]}
    ]},
    {id: 2, title: 'hello', parent: 0, children: [
        {id: 8, title: 'hello', parent: 2}
    ]}
]

Please help me with a recursive function to do this in node.js.

Following is the recursive function is what I have tried:

    function getNestedChildren(arr, parent) {
    var out = []
    for(var i in arr) {
        if(arr[i].parent.number == parent.number) {
            var children = getNestedChildren(arr, arr[i].id)

            if(children.length) {
                arr[i].children = children
            }
            out.push(arr[i])
        }
    }
    return out
}

Please help me to solve this. I am a newbie in this.

What have you tried? We aren't really a coding service. You really ought to make some attempts yourself and then ask us questions about where you got stuck. — jfriend00
– jfriend00, Commented Dec 11, 2017 at 3:47
This is what I have tried but could not upload it.function getNestedChildren(arr, parent) { var out = [] for(var i in arr) { if(arr[i].parent.number == parent.number) { var children = getNestedChildren(arr, arr[i].id) if(children.length) { arr[i].children = children } out.push(arr[i]) } } return out } — Sahaja
– Sahaja, Commented Dec 11, 2017 at 3:51
Welcome to stack overflow. Please put the code you tried into your question, format it properly and then explain what result you got or where you got stuck and more specifically what you want help with in that code. Multiline code is not legible in comments. You can use the "edit" button to edit your question to add the code you tried and the additional explanation. — jfriend00
– jfriend00, Commented Dec 11, 2017 at 3:58

traktor · Accepted Answer · 2017-12-11 06:17:15Z

5

Renaming some variables helped me solve this.

getNestedChildren returns an array of children, so rename out to children.
the children returned by the recursive call are the grandchildren of the parent being processed in the call. So call the result of the recursive call grandchildren.

The problem that caused the code to not work:

line 4 of the posted code uses the id property of the parent parameter. So either ensure that every call to getNestedChidren provides an object with such a property (as below), or change the second argument to parentNumber and just supply the numeric value of the number property. Your choice.

Lastly, avoid using for ... in loops to iterate an array - please do a web search for more information and discussion.

var array = [
    {id: 1, title: 'hello', parent: {number:0}},
    {id: 2, title: 'hello', parent: {number:0}},
    {id: 3, title: 'hello', parent: {number:1}},
    {id: 4, title: 'hello', parent: {number:3}},
    {id: 5, title: 'hello', parent: {number:4}},
    {id: 6, title: 'hello', parent: {number:4}},
    {id: 7, title: 'hello', parent: {number:3}},
    {id: 8, title: 'hello', parent: {number:2}}
]
function getNestedChildren(arr, parent) {
    var children = [];
    for(var i =0; i < arr.length; ++i) {
        if(arr[i].parent.number == parent.number) {
            var grandChildren = getNestedChildren(arr, {number: arr[i].id})

            if(grandChildren.length) {
                arr[i].children = grandChildren;
            }
            children.push( arr[i]);
        }
    }
    return children;
}
var nest = getNestedChildren(array,{number: 0});
console.log( nest);

answered Dec 11, 2017 at 6:17

traktor

19.7k5 gold badges37 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user992731 Over a year ago

@traktor53 - How would solve this if your array was more flat?

JimmyTheCode Over a year ago

I couldn't comment all that code here, so I wrote a separate answer.

traktor · Accepted Answer · 2021-05-16 23:02:22Z

4

In case anyone wants to know the solution with a flattened initial array, as per user992731's request:

var array = [
    {id: 1, title: 'hello', parent: 0},
    {id: 2, title: 'hello', parent: 0},
    {id: 3, title: 'hello', parent: 1},
    {id: 4, title: 'hello', parent: 3},
    {id: 5, title: 'hello', parent: 4},
    {id: 6, title: 'hello', parent: 4}
];

function getNestedChildren(arr, parent) {
    var children = [];
    for(var i =0; i < arr.length; ++i) {
        if(arr[i].parent == parent) {
            var grandChildren = getNestedChildren(arr, arr[i].id);
            if(grandChildren.length) {
                arr[i].children = grandChildren;
            }
            children.push(arr[i]);
        }
    }
    return children;
}
var nest = getNestedChildren(array,0);
console.log(nest);

edited May 16, 2021 at 23:02

traktor

19.7k5 gold badges37 silver badges56 bronze badges

answered May 16, 2021 at 7:55

JimmyTheCode

6,0308 gold badges57 silver badges113 bronze badges

Comments

Scott Sauyet · Accepted Answer · 2023-04-13 13:10:28Z

This old question was resurrected by an new answer, which has since been deleted.

But I thought it's worth adding a simpler solution:

const nest = (xs, id = 0) => xs
  .filter (x => x .parent .number == id )
  .map ((x) => ({...x, children: nest (xs, x. id)}))

const input = [{id: 1, title: 'hello', parent: {number:0}}, {id: 2, title: 'hello', parent: {number:0}}, {id: 3, title: 'hello', parent: {number:1}}, {id: 4, title: 'hello', parent: {number:3}}, {id: 5, title: 'hello', parent: {number:4}}, {id: 6, title: 'hello', parent: {number:4}}, {id: 7, title: 'hello', parent: {number:3}}, {id: 8, title: 'hello', parent: {number:2}}]

console .log (nest (input))

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

Our function creates a tree by accepting a flat list and the root id (defaulted to 0), filtering to find all elements with matching parent id, then for each one, adding its children by recurring using the current element's id as the root. Note that we don't need an explicit base case, because filter will simply return an empty array when we're done, and hence we won't recur in the map call.

Note that this includes an empty children array in the leaf nodes. If that's a problem, a slightly more complex variant will skip them:

const nest = (xs, id = 0) => xs
  .filter (x => x .parent .number == id)
  .map ((x) => (
    (children = nest (xs, x .id)) => ({...x, ...(children .length ? {children} : {})})
  )())

const input = [{id: 1, title: 'hello', parent: {number:0}}, {id: 2, title: 'hello', parent: {number:0}}, {id: 3, title: 'hello', parent: {number:1}}, {id: 4, title: 'hello', parent: {number:3}}, {id: 5, title: 'hello', parent: {number:4}}, {id: 6, title: 'hello', parent: {number:4}}, {id: 7, title: 'hello', parent: {number:3}}, {id: 8, title: 'hello', parent: {number:2}}]

console .log (nest (input))

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

Collectives™ on Stack Overflow

Create a nested array recursively in Node.js

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related