Lodash _.flatMapDepth 返回深度嵌套的对象数组

Question

i am trying to get an array from deep level nested structure, i was able to get one level. Even if i pass depth as 4 also i am not able to get.

any help is appreciated

input

let a = [{b: [{c: [{d: [{e: "name"}]}]}]}]

tried snippet

   let output = _.flatMapDepth(a, 'e', 3);

getting empty array

i need to get as below, using lodash

output = [{e: "name"}]

any help is appreciated

Answer 1

better use _().flatMap

 let a = [{b: [{c: [{d: [{e: "name"}]}]}]}];
console.log(a);
let output1 = _(a).flatMap('b').flatMap('c').flatMap('d').value();
console.log(output1); // [ { e: 'name' } ]
let output2 = _(a).flatMap('b').flatMap('c').flatMap('d').flatMap('e').value();
console.log(output2); // [ 'name' ]

This one goes through the nested objects and resolves them!

Answer 2

From the Lodash docs :

_.flatMapDepth

// _.flatMapDepth(collection, [iteratee=_.identity], [depth=1])

function duplicate(n) {
  return [[[n, n]]];
}

_.flatMapDepth([1, 2], duplicate, 2);
// => [[1, 1], [2, 2]]

and _.identity

// _.identity(value)

var object = { 'a': 1 };

console.log(_.identity(object) === object);
// => true

I think this should help.

---

If this does not help. I have written a JavaScript solution to your problem:

 let a = [{ b: [{ c: [{ d: [{ e: "name" }] }] }] }, { b: [{ c: [{ d: [{ e: "age" }] }] }] }]; function getDeepKeys(arr, key, maxDepth = 8) { let res = []; let depth = 0; for (let i = 0; i < arr.length; i++) { const obj = arr[i]; if (typeof obj !== "object" || obj == null) { continue; } for (const k in obj) { if (obj.hasOwnProperty(k)) { const element = obj[k]; if (k === key) { res.push(obj); // can also be res.push(element) // if you want the contents of obj to be added to the resulting array continue; } else if (depth <= maxDepth) { res = getDeepKeys(element, key).concat(res); depth++; } } } } return res; } let keys = getDeepKeys(a, "e"); console.log(keys);

Be careful, though. If there's an object without the e key, you will get an infinite loop error. Therefor I created the depth and maxDepth variable. You can adjust this value like so: getDeepKeys(a, "e", 12); (now the maxDepth equals 12 instead of the default value of 10).