Create nested object from flat array

Question

I currently have an array of objects which I'm trying to reshape into a nested object with the ID as an object key, and target that ID with the parent id if it's not "0". I've tried several approaches but I'm struggling big time! The main stumbling block for me is anything beyond one or two layers deep. Ideally I need this to be dynamic so it can handle potentially any depth although in the wild I doubt it will go beyond 3 layers.

Here is the incoming array of objects:

[
 {
 ID: "1671",
 parent: "0",
 },
 {
 ID: "1223",
 parent: "0",
 },
 {
 ID: "1668",
 parent: "0",
 },
 {
 ID: "1688",
 parent: "0",
 },
 {
 ID: "1669",
 parent: "0",
 },
 {
 ID: "1681",
 parent: "1669",
 },
 {
 ID: "1680",
 parent: "1669",
 },
 {
 ID: "1670",
 parent: "1669",
 },
 {
 ID: "1682",
 parent: "1669",
 },
 {
 ID: "1433",
 parent: "1682",
 },
 {
 ID: "1684",
 parent: "1682",
 },
 {
 ID: "1672",
 parent: "1684",
 },
 {
 ID: "1685",
 parent: "1672",
 },
 {
 ID: "1686",
 parent: "1672",
 },
 {
 ID: "1683",
 parent: "0",
 },
 {
 ID: "1230",
 parent: "0",
 },
 {
 ID: "1667",
 parent: "0",
 },
 {
 ID: "1687",
 parent: "0",
 }
];

And here is the desired transformation:

1671: {
 ID: "1671",
 parent: "0",
 },
 1223: {
 ID: "1223",
 parent: "0",
 },
 1668: {
 ID: "1668",
 parent: "0",
 },
 1688: {
 ID: "1688",
 parent: "0",
 },
 1669: {
 ID: "1669",
 parent: "0",
 children: {
 1681: {
 ID: "1681",
 parent: "1669",
 },
 1680: {
 ID: "1680",
 parent: "1669",
 },
 1670: {
 ID: "1670",
 parent: "1669",
 },
 1682: {
 ID: "1682",
 parent: "1669",
 children: {
 1433: {
 ID: "1433",
 parent: "1682",
 },
 1684: {
 ID: "1684",
 parent: "1682",
 children: {
 1672: {
 ID: "1672",
 parent: "1684",
 children: {
 1685: {
 ID: "1685",
 parent: "1672",
 },
 1686: {
 ID: "1686",
 parent: "1672",
 }
 }
 }
 }
 }
 }
 }
 }
 },
 1683: {
 ID: "1683",
 parent: "0",
 },
 1230: {
 ID: "1230",
 parent: "0",
 },
 1667: {
 ID: "1667",
 parent: "0",
 },
 1687: {
 ID: "1687",
 parent: "0",
 }

Most of my failed approaches have been using Array.reduce() and other types of recursion but to no avail, so I'm interested to see if there is a solution for this.

Thanks

• Nina Scholz: please add your try/tries.

Answer 1

You can use recursive function like this:

function findFor(parentId) {
 // create a new object to store the result
 var z = {};
 // for each item in a
 for (var i = 0; i<a.length; i++){
 // find all children of parentId
 if (a[i].parent === parentId) {
 // recursively find children for each children of parentId
 var ch = findFor(a[i].ID);
 // if it has no children, skip adding the children prop
 var o = Object.keys(ch).length === 0 ? {} : { children: ch };
 z[a[i].ID] = Object.assign(o, a[i]);
 }
 }
 return z;
}
// find all item whose parent is "0"
console.log(findFor("0"));

var a = [
 { ID: "1671", parent: "0", },
 { ID: "1223", parent: "0", },
 { ID: "1668", parent: "0", },
 { ID: "1688", parent: "0", },
 { ID: "1669", parent: "0", },
 { ID: "1681", parent: "1669", },
 { ID: "1680", parent: "1669", },
 { ID: "1670", parent: "1669", },
 { ID: "1682", parent: "1669", },
 { ID: "1433", parent: "1682", },
 { ID: "1684", parent: "1682", },
 { ID: "1672", parent: "1684", },
 { ID: "1685", parent: "1672", },
 { ID: "1686", parent: "1672", },
 { ID: "1683", parent: "0", },
 { ID: "1230", parent: "0", },
 { ID: "1667", parent: "0", },
 { ID: "1687", parent: "0", }
];
function findFor(parentId) {
 var z = {};
 for (var i = 0; i<a.length; i++){
 if (a[i].parent === parentId) {
 var ch = findFor(a[i].ID);
 var o = Object.keys(ch).length === 0 ? {} : { children: ch };
 z[a[i].ID] = Object.assign(o, a[i]);
 }
 }
 
 return z;
}
console.log(findFor("0"));

Answer 2

A single loop non recursive approach by respecting the parents.

var flat = [{ ID: "1671", parent: "0" }, { ID: "1223", parent: "0" }, { ID: "1668", parent: "0" }, { ID: "1688", parent: "0" }, { ID: "1669", parent: "0" }, { ID: "1681", parent: "1669" }, { ID: "1680", parent: "1669" }, { ID: "1670", parent: "1669" }, { ID: "1682", parent: "1669" }, { ID: "1433", parent: "1682" }, { ID: "1684", parent: "1682" }, { ID: "1672", parent: "1684" }, { ID: "1685", parent: "1672" }, { ID: "1686", parent: "1672" }, { ID: "1683", parent: "0" }, { ID: "1230", parent: "0" }, { ID: "1667", parent: "0" }, { ID: "1687", parent: "0" }],
 tree = function (data, root) {
 var o = {};
 data.forEach(function(a) {
 a = Object.assign({}, a);
 if (o[a.ID] && o[a.ID].children) {
 a.children = o[a.ID].children;
 }
 o[a.ID] = { [a.ID]: a };
 o[a.parent] = o[a.parent] || {};
 o[a.parent][a.parent] = o[a.parent][a.parent] || {};
 o[a.parent][a.parent].children = o[a.parent][a.parent].children || {};
 o[a.parent][a.parent].children[a.ID] = a;
 });
 return o[root][root].children;
 }(flat, '0');
console.log(tree);

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• Nina Scholz: the levels are not restricted.