CODEWITHSUNDEEP
javascriptlodash
Sgt Maddonut
Sgt Maddonut

Reputation: 779

How to merge two arrays and sum values of duplicate objects using lodash

There are two arrays:

[
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 1},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 5},
  {"id": "342343343t4t34rwefewfd53", "quantity": 3}
]

and

[
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 2},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 1}
]

How to combine them into one summing quantity?

[
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 3},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 6},
  {"id": "342343343t4t34rwefewfd53", "quantity": 3}
]

One of them can be empty sometimes

Upvotes: 10

Views: 7520

Answers (7)

chaserino
chaserino

Reputation: 304

This function uses lodash reduce and mapValues to sum the specified keys of an array of objects into a single result object. It allows missing keys in each object.

const mergeAndSumObjVals = (objs, keys) => _.reduce(
  objs,
  (o, s) => _.mapValues(o, (v, k) => (v || 0) + (s[k] || 0)),
  _.chain(keys).invert().mapValues(() => 0).value(),
)


const objs = [{
  negative: 54,
  positive: 2
}, {
  inconclusive: 8,
  positive: 1
}, {
  negative: 26,
  inconclusive: 5,
  positive: 4
}]

const result = mergeAndSumObjVals(objs, ['negative', 'inconclusive', 'positive'])

console.log(result)
<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>

Upvotes: 0

Jono
Jono

Reputation: 4076

All these answers require you to know the object structure to select and sum.

lodash does actually allow you to do this without knowing the structure; by using the customizer parameter of _.mergeWidth;

let result = _.mergeWith(arr1, arr2, (objValue, srcValue, key, object, source, stack) =>{
    
    //Add any conditions you need here. Ive added a few relevant examples. 
    //if(key.startsWith("num")) //Check for property name prefixes like num...
    //if(propertyNamesToSum.Includes(key)) //check if your property is in your predefined list of property names
    //This one below sums any properties that are numbers
    if(_.isNumber(srcValue) && _.isNumber(objValue)){
        return srcValue + objValue;
    } 
    return undefined; //lodash will merge as usual if you return undefined. 

});

Lodash docs - https://lodash.com/docs/4.17.15#mergeWith

Upvotes: 2

Prince Sumberia
Prince Sumberia

Reputation: 37

You can use .reduce and .find methods to achieve this.

const arr1 = [{"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 1}, {"id": "344430b94t4t34rwefewfdff", "quantity": 5}, {"id": "342343343t4t34rwefewfd53", "quantity": 3}];
const arr2 = [{"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 2}, {"id": "344430b94t4t34rwefewfdff", "quantity": 1}];

const result =  [...arr1, ...arr2].reduce((accumulator, currentValue) => {
  const element = accumulator.find(item => item.id === currentValue.id)
  element ? element.quantity += currentValue.quantity : accumulator.push(currentValue)
  return accumulator
},[])

console.log(result)

Upvotes: 1

JanuszO
JanuszO

Reputation: 1240

Version with additional object keys. The body of the function does not interfere with what object has properties. So sum by "qty" and check by "prop"

var first = [ 
  {quantity:100, id:1, variantId: 1}, 
  {quantity:300, id:2, variantId: 2, propA: 'aaa'},

];

var second = [
  {quantity:100, id:1, variantId: 1},
  {quantity:200, id:2, variantId: 2, propB: true}, 
  {quantity:300, id:3, variantId: 3, propC: 'ccc'}, 
]

function mergeArrays(arrayOfArrays, propToCheck, propToSum) {
    let sum = [];
    [].concat(...arrayOfArrays).map(function(o) {
        
        let existing = sum.filter(function(i) { return i[propToCheck] === o[propToCheck] })[0];
    
        if (!existing) {

            sum.push(o);
        } else {

            existing[propToSum] += o[propToSum];
            
            let copyProps = Object.keys(o).filter(obj => {
                  return existing[obj] !== o[obj]
            }).map(val => (val !== propToSum) ? existing[val] = o[val] : null)
        }
             
    });

    return sum;
}

console.log(mergeArrays([first, second], 'variantId', 'quantity'))

Upvotes: 0

Andy
Andy

Reputation: 63524

You can use lodash but modern vanilla JS is just as viable and performant. I would imagine the other answers will be using functional methods like reduce, so here's a version that uses a simple for/of loop with find rather than a dictionary lookup which might be longer, but it is a little easier to follow.

const arr1 = [{"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 1}, {"id": "344430b94t4t34rwefewfdff", "quantity": 5}, {"id": "342343343t4t34rwefewfd53", "quantity": 3}];
const arr2 = [{"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 2}, {"id": "344430b94t4t34rwefewfdff", "quantity": 1}];

function merge(arr1, arr2) {

  // Merge the arrays, and set up an output array.
  const merged = [...arr1, ...arr2];
  const out = [];

  // Loop over the merged array
  for (let obj of merged) {

    // Destructure the object in the current iteration to get
    // its id and quantity values
    const { id, quantity } = obj;

    // Find the object in out that has the same id
    const found = out.find(obj => obj.id === id);

    // If an object *is* found add this object's quantity to it...
    if (found) {
      found.quantity += quantity;

    // ...otherwise push a copy of the object to out
    } else {
      out.push({ ...obj });
    }
  }
  
  return out;

}

console.log(merge(arr1, arr2));

Upvotes: 4

jo_va
jo_va

Reputation: 13963

You can do it with plain JavaScript.

Use Array.reduce() to make an intermediate dictionary by id and accumulate the quantities, then turn it into an array with Object.values():

const arr1 = [
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 1},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 5},
  {"id": "342343343t4t34rwefewfd53", "quantity": 3}
];
const arr2 = [
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 2},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 1}
];

const result = Object.values([...arr1, ...arr2].reduce((acc, { id, quantity }) => {
  acc[id] = { id, quantity: (acc[id] ? acc[id].quantity : 0) + quantity  };
  return acc;
}, {}));

console.log(result);

Upvotes: 13

Terry Lennox
Terry Lennox

Reputation: 30685

You can just do this with reduce:

let a1 = [
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 2},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 1}
];

let a2 = [
  {"id": "5c5030b9a1ccb11fe8c321f4", "quantity": 1},
  {"id": "344430b94t4t34rwefewfdff", "quantity": 5},
  {"id": "342343343t4t34rwefewfd53", "quantity": 3}
];

let result = Object.values(a1.concat(a2).reduce((acc, v) => {
   if (!acc[v.id]) {
       acc[v.id] = {id: v.id, quantity: 0};
   }
   acc[v.id].quantity += v.quantity;
   return acc;
}, {}));

console.log("Results: ", result);

Upvotes: 2

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