JavaScript flattening an array of arrays of objects

Question

I have an array which contains several arrays, each containing several objects, similar to this.

[[object1, object2],[object1],[object1,object2,object3]]

Here is a screenhot of the object logged to the console.

What would be the best approach to flattening this out so it just an array of objects?

I've tried this with no luck:

console.log(searchData);  
  var m = [].concat.apply([],searchData);    
console.log(m);

searchData logs out the screenshot above, but m logs out [ ]

Here is the actual contents of searchData:

[[{"_id":"55064111d06b96d974937a6f","title":"Generic Title","shortname":"generic-title","contents":"<p>The Healing Center offers practical, social, and spiritual support to individuals and families. Services include, but are not limited to: food and clothing, job skills training and job search assistance, auto repair (Saturdays only), mentoring, financial counseling, tutoring, prayer, life skills training, and helpful information about local community services.</p><p>Stay in touch with us:</p>","__v":0},{"_id":"5508e1405c621d4aad2d2969","title":"test english","shortname":"test-page","contents":"<h2>English Test</h2>","__v":0}],[{"_id":"550b336f33a326aaee84f883","shortname":"ok-url","title":"now english","contents":"<p>okokko</p>","category":"Transportation","__v":0}]]

Answer 1

You can use Array.concat like bellow:-

var arr = [['object1', 'object2'],['object1'],['object1','object2','object3']];
var flattened = [].concat.apply([],arr);

flattened will be your expected array.

Answer 2

A recursive solution for deep (nested) flattening:

function flatten(a) {
  return Array.isArray(a) ? [].concat.apply([], a.map(flatten)) : a;
}

A bit more compactly with ES6:

var flatten = a => Array.isArray(a) ? [].concat(...a.map(flatten)) : a;

For fun, using a generator named F for "flatten", to lazily generate flattened values:

function *F(a) {
  if (Array.isArray(a)) for (var e of a) yield *F(e); else yield a;
}

>> console.log(Array.from(F([1, [2], 3])));
<< [ 1, 2, 3 ]

For those not familiar with generators the yield * syntax yields values from another generator. Array.from takes an iterator (such as results from invoking the generator function) and turns it into an array.

Answer 3

If you only need simple flatten, this may works:

var arr = [['object1', 'object2'],['object1'],['object1','object2','object3']];
var flatenned = arr.reduce(function(a,b){ return a.concat(b) }, []);

For more complex flattening, Lodash has the flatten function, which maybe what you need: https://lodash.com/docs#flatten

//Syntax: _.flatten(array, [isDeep])

_.flatten([1, [2, 3, [4]]]);
// → [1, 2, 3, [4]];

// using `isDeep` to recursive flatten
_.flatten([1, [2, 3, [4]]], true);
// → [1, 2, 3, 4];

Answer 4

Recursively flatten an array:

function flatten(array) {
   return !Array.isArray(array) ? array : [].concat.apply([], array.map(flatten));
}
 
var yourFlattenedArray = flatten([[{"_id":"55064111d06b96d974937a6f","title":"Generic Title","shortname":"generic-title","contents":"<p>The Healing Center offers practical, social, and spiritual support to individuals and families. Services include, but are not limited to: food and clothing, job skills training and job search assistance, auto repair (Saturdays only), mentoring, financial counseling, tutoring, prayer, life skills training, and helpful information about local community services.</p><p>Stay in touch with us:</p>","__v":0},{"_id":"5508e1405c621d4aad2d2969","title":"test english","shortname":"test-page","contents":"<h2>English Test</h2>","__v":0}],[{"_id":"550b336f33a326aaee84f883","shortname":"ok-url","title":"now english","contents":"<p>okokko</p>","category":"Transportation","__v":0}]]
);

log(yourFlattenedArray);

function log(data) {
  document.write('<pre>' + JSON.stringify(data, null, 2) + '</pre><hr>');
}

* {font-size: 12px; }

Answer 5

let functional = {
    flatten (array) {
        if (Array.isArray(array)) {
            return Array.prototype.concat(...array.map(this.flatten, this));
        }

        return array;
    }
};

functional.flatten([0, [1, 2], [[3, [4]]]]); // 0, 1, 2, 3, 4

Answer 6

Using ES6 Spread Operator

Array.prototype.concat(...searchData)

OR

[].concat(...searchData)

Answer 7

I've noticed that people are using recursions which are not cost friendly, especially with new ES6 standards giving us the power of spread operators. When you're pushing the items into the master array just use ... and it will automatically add flattened objects. Something like

array.push(...subarray1)    // subarray1 = [object1, object2]
array.push(...subarray2)    // subarray2 = [object3]
array.push(...subarray3)    // subarray3 = [object4,object5, object6]
// output -> array = [object1, object2, object3, object4, object5, object6]

Answer 8

let nestedArray = [[1, 2], [3, 4], [5, 6]];

let flattenArray = function(nestedArray) {

	let flattenArr = [];
  
	nestedArray.forEach(function(item) {
  	flattenArr.push(...item);
  });
  
  return flattenArr;
};

console.log(flattenArray(nestedArray)); // [1, 2, 3, 4, 5, 6]

Answer 9

var arr = [1,[9,22],[[3]]];
var res = [];

function flatten(arr){
for(let i=0;i<arr.length;i++){
if(typeof arr[i] == "number"){
res.push(arr[i]);
}
else if(typeof arr[i] == "object"){
fatten(arr[i]);
}
}
}

Calling function

flatten(arr);
console.log(res);

Result  

[1, 9, 22, 3]

Answer 10

you can use flat() :

const data = [ [{id:1}, {id:2}], [{id:3}] ];
const result = data.flat();
console.log(result);

// you can specify the depth

const data2 = [ [ [ {id:1} ], {id:2}], [{id:3}] ];
const result2 = data2.flat(2);

console.log(result2);

in your case :

const data = [[{"_id":"55064111d06b96d974937a6f","title":"Generic Title","shortname":"generic-title","contents":"<p>The Healing Center offers practical, social, and spiritual support to individuals and families. Services include, but are not limited to: food and clothing, job skills training and job search assistance, auto repair (Saturdays only), mentoring, financial counseling, tutoring, prayer, life skills training, and helpful information about local community services.</p><p>Stay in touch with us:</p>","__v":0},{"_id":"5508e1405c621d4aad2d2969","title":"test english","shortname":"test-page","contents":"<h2>English Test</h2>","__v":0}],[{"_id":"550b336f33a326aaee84f883","shortname":"ok-url","title":"now english","contents":"<p>okokko</p>","category":"Transportation","__v":0}]]

const result = data.flat();

console.log(result);