We have data with a one to many relationships in the same array. The organization is established by level. An element's parent is always one level higher than itself and is referenced by parentId.
We are required to get a multi-level array from this array. The elements with the highest level would be the main array, with their children as subarray.
If the input array is given by −
const arr = [
{
_id: 100,
level: 3,
parentId: null,
},
{
_id: 101,
level: 2,
parentId: 100,
},
{
_id: 102,
level: 2,
parentId: 100,
},
{
_id: 103,
level: 2,
parentId: 100,
},
{
_id: 104,
level: 1,
parentId: 101,
},
{
_id: 105,
level: 1,
parentId: 102,
},
{
_id: 106,
level: 1,
parentId: 101,
},
{
_id: 107,
level: 1,
parentId: 103,
},
{
_id: 108,
level: 1,
parentId: 102,
},
{
_id: 109,
level: 1,
parentId: 103,
}
];Then the output structure should be something like −
100 | ------------------------------------ | | | 101 102 103 ------- ------ ------ | | | | | | 104 106 105 108 107 109
Example
The code for this will be −
const arr = [{
_id: 100,
level: 3,
parentId: null,
},
{
_id: 101,
level: 2,
parentId: 100,
},
{
_id: 102,
level: 2,
parentId: 100,
},
{
_id: 103,
level: 2,
parentId: 100,
},
{
_id: 104,
level: 1,
parentId: 101,
},
{
_id: 105,
level: 1,
parentId: 102,
},
{
_id: 106,
level: 1,
parentId: 101,
},
{
_id: 107,
level: 1,
parentId: 103,
},
{
_id: 108,
level: 1,
parentId: 102,
},
{
_id: 109,
level: 1,
parentId: 103,
}];
const prepareTree = (arr = [], root = null) => {
let res;
const obj = Object.create(null);
arr.forEach(el => {
el.children = obj[el._id] && obj[el._id].children;
obj[el._id] = el;
if (el.parentId === root) {
res = el;
}
else {
obj[el.parentId] = obj[el.parentId] || {};
obj[el.parentId].children = obj[el.parentId].children || [];
obj[el.parentId].children.push(el);
}
});
return res;
};
console.log(JSON.stringify(prepareTree(arr), undefined, 4));Output
And the output in the console will be −
{
"_id": 100,
"level": 3,
"parentId": null,
"children": [
{
"_id": 101,
"level": 2,
"parentId": 100,
"children": [
{
"_id": 104,
"level": 1,
"parentId": 101
},
{
"_id": 106,
"level": 1,
"parentId": 101
}
]
},
{
"_id": 102,
"level": 2,
"parentId": 100,
"children": [
{
"_id": 105,
"level": 1,
"parentId": 102
},
{
"_id": 108,
"level": 1,
"parentId": 102
}
]
},
{
"_id": 103,
"level": 2,
"parentId": 100,
"children": [
{
"_id": 107,
"level": 1,
"parentId": 103
},
{
"_id": 109,
"level": 1,
"parentId": 103
}
]
}
]
}