Method to merge / join two or more arrays of objects by key javascript

Question

I am trying to merge two or more arrays but its not working as I am wanting.

I have two arrays arrCustomer and arrCustomerDetails. Both arrays have CustomerID as a key but I am wanting all values from arrCustomerDetails with merged in properties from the array arrCustomer. I tried using _merge but its giving my only the count of the arrCustomer.

Example:

const arrCustomer = [
    { id: 1, name: "a" },
    { id: 2, name: "b" },
    { id: 3, name: "c" }
];

const arrCustomerDetail = [
    { id: 1, location: "jupiter", group: "C" },
    { id: 1, location: "venus", group: "G" },
    { id: 2, location: "mars", group: "D" }
];

const expecteResult = [
    { id: 1, name: "a", location: "jupiter", group: "C" },
    { id: 1, name: "a", location: "venus", group: "G" },
    { id: 2, name: "b", location: "mars", group: "D" },
    { id: 3, name: "c"  location: "", group: "" }
]

This works but its slow:

 let combinedData = [];
      arrCustomerDetail.map((element) => {
        combinedData.push({
          ...element,
          ...arrCustomer.find(
            (customer) => customer.id=== element.id
          ),
        });
      });

      arrCustomer.map((customer) => {
        if (
          combinedData.findIndex(
            (detail) => detail.id=== customer.id
          ) === -1
        )
          combinedData.push({
            ...customer,
          });
      });

Thanks all

Answer 1

( Join / Merge / Combine ) multiple arrays of objects combined by key.

Update, it is also possible to make this join at run time for more than one array. you just need to define a primary matrix and create a filter on a matrix of matrices, follow this example in.

I hope this example helps, it worked perfectly, for the examples you gave, just edit the example below and you will see the result, I even made a joke doing the merging of everything and it worked correctly. Remembering that it will always look at a primary matrix as a base.

"use strict";
const arrCustomer1 = [
    { id: 1, name: "a" },
    { id: 2, name: "b" }
];
const arrCustomerDetail1 = [
    { id: 1, location: "jupiter", group: "C" },
    { id: 2, location: "mars", group: "D" }
];
const wantedArray1 = [
    { id: 1, name: "a", location: "jupiter", group: "C" },
    { id: 2, name: "b", location: "mars", group: "D" }
];
const arrCustomer2 = [
    { id: 1, name: "a" },
    { id: 2, name: "b" },
    { id: 3, name: "c" }
];
const arrCustomerDetail2 = [
    { id: 1, location: "jupiter", group: "C" },
    { id: 2, location: "mars", group: "D" }
];
const wantedArray2 = [
    { id: 1, name: "a", location: "jupiter", group: "C" },
    { id: 2, name: "b", location: "mars", group: "D" },
    { id: 3, name: "c" } //or blanks for the other fields location group
];
const arrCustomer3 = [
    { id: 1, name: "a" },
    { id: 2, name: "b" },
    { id: 3, name: "c" }
];
const arrCustomerDetail3 = [
    { id: 1, location: "jupiter", group: "C" },
    { id: 1, location: "venus", group: "G" },
    { id: 2, location: "mars", group: "D" }
];
const wantedArray3 = [
    { id: 1, name: "a", location: "jupiter", group: "C" },
    { id: 1, name: "a", location: "venus", group: "G" },
    { id: 2, name: "b", location: "mars", group: "D" },
    { id: 3, name: "c" } //or blanks for the other fields location group
];

const combinedArrays = [arrCustomerDetail1,
    wantedArray1,
    arrCustomer2,
    arrCustomerDetail2,
    wantedArray2,
    arrCustomer3,
    arrCustomerDetail3,
    wantedArray3];

function joinArrByKey(primaryArr, combinedArrays, key) {
    return primaryArr.map((eArr1) => {
        const filter = new Array().concat.apply([], combinedArrays).filter((eArr2) => eArr2.id === eArr1[key]);
        return filter.length ? Object.assign({}, eArr1, ...filter) : eArr1;
    });
}

console.log(joinArrByKey(arrCustomer1, combinedArrays, 'id'));

console.log(joinArrByKey(arrCustomer2, combinedArrays, 'id'));

console.log(joinArrByKey(arrCustomer3, combinedArrays, 'id'));

( Join / Merge / Combine ) Only for two arrays by key id, faster.

you can create your own function like this and share it with all applications, instead of using _lodash.

"use strict";
const arr1 = [
    { id: 1, name: "a" },
    { id: 2, name: "b" },
];
const arr2 = [
    { id: 1, price: 10 },
    { id: 2, price: 20 },
];
function joinArrById(primaryArr, secondArray) {
    return primaryArr.map((eArr1) => {
        const find = secondArray.find((eArr2) => eArr2.id === eArr1.id);
        return find ? Object.assign(Object.assign({}, eArr1), find) : eArr1;
    });
}
console.log(joinArrById(arr1, arr2));

If the solution above doesn't suit you, a solution with _lodash.

import * as _ from "lodash";

const arr1 = [
  { id: 1, name: "a" },
  { id: 2, name: "b" },
];
const arr2 = [
  { id: 1, price: 10 },
  { id: 2, price: 20 },
];

var arrJoin = _.map(arr1, (obj: { id: number }) => {
  return _.assign(
    obj,
    _.find(arr2, {
      id: obj.id,
    })
  );
});

console.log(arrJoin);

Answer 2

Lodash doesn't really support merging lists together and keying off an object property to do so. I would do something like this, and roll my own merge() function.

[Note: this merge() function runs in linear time — O(n).]

const _ = require('lodash');

function merge(selectKey, keyComparer, ...lists) {
  const map = new Map();

  for (const list of lists) {
    for (const item of list) {

      const key = selectKey(item);
      let value = map.get(key);

      if (value === undefined) {
        map.set(key, [item]);
      }
      else {
        value.push(item);
      }
    }
  }

  const merged = Array.from(map.keys())
    .sort(keyComparer)
    .map( k => _.merge( {}, ...map.get(k) ) );
  return merged;
}

where * selectKey is a function that is passed an object and returns its key, and * keyComparer is a function that accepts two keys, x and y and returns a numeric indication of whether x is less than, equal to, or greater than `y'. The convention is that

• return values < 0 indicate that x is less than y
• return values of 0 indicate that x and y are equal
• return values > 0 indicate x is greater than y

Once you have that, it's easy:

const arr1 = [
  { id: 1, name: 'a' },
  { id: 2, name: 'b' },
  { id: 3, name: 'c' },
];
const arr2 = [
  { id: 1, location: 'jupiter', group: 'C' },
  { id: 4, location: 'venus', group: 'E' },
  { id: 2, location: 'mars', group: 'D' },
];

const idComparer = (x, y) => Math.sign(x - y);
const selectKey = o => o.id;

const merged = merge(selectKey, idComparer, arr1, arr2 );

The return value here is

[
  { id: 1 , name: "a" , location: "jupiter" , group: "C" } ,
  { id: 2 , name: "b" , location: "mars"    , group: "D" } ,
  { id: 3 , name: "c"                                    } ,
  { id: 4 ,             location: "venus"   , group: "E" } ,
]