How find sum of values in array of objects with specific distinct value pair?

Question

I want to find sum of values in an array of objects with specific user and create a different array of objects with total value for the particular user.

This is the Array of objects that I have.

var userData = [
  {name: "user1", amount: 80},
  {name: "user1", amount: 12},
  {name: "user1", amount: 8},
  {name: "user2", amount: 60},
  {name: "user2", amount: 12},
  {name: "user3", amount: 90},
  {name: "user3", amount: 28}
]

The out put that I need.

UserGrandTotal = [
  {name: "user1", totalamount: 100},
  {name: "user2", totalamount: 72},
  {name: "user3", totalamount: 118}  
]

Please provide the JavaScript that you have tried as a minimal reproducible example — zer00ne
– zer00ne, Commented Jan 29, 2020 at 19:45

Mihai Alexandru-Ionut · Accepted Answer · 2020-01-29 20:09:41Z

5

You could use reduce method for this by passing a callback provided function which is applied for every item in the array.

I created an hash structure using reduce where I stored every unique name as hash key and, as hash value, we have user details with total amount for that specified user.

As complexity of the algorithm, we have O(N) because we're iterating the whole array only once.

var userData = [ {name: "user1", amount: 80}, {name: "user1", amount: 12}, {name: "user1", amount: 8}, {name: "user2", amount: 60}, {name: "user2", amount: 12}, {name: "user3", amount: 90}, {name: "user3", amount: 28} ]; 

var result = Object.values(userData.reduce((hash, item) => {
    if (!hash[item.name]) {
        hash[item.name] = { name: item.name, amount: 0 };
    }
    hash[item.name].amount += item.amount;
    return hash;
}, {}));
console.log(result);

edited Jan 29, 2020 at 20:09

answered Jan 29, 2020 at 19:46

Mihai Alexandru-Ionut

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4 Comments

The fourth bird Over a year ago

Out of curiosity, why do you use reduce and push the result to a separate variable instead of using a foreach?

Mihai Alexandru-Ionut Over a year ago

@Thefourthbird, I updated my answer with a simple hash structure.

Mihai Alexandru-Ionut Over a year ago

Yes, forEach could be another option, but using reduce we don't need to declare an optional variable result = [].

Mihai Alexandru-Ionut Over a year ago

Also, with reduce we can use a shorter way with comma operator :

var result = Object.values(userData.reduce((hash, item) => (!hash[item.name] ? (hash[item.name] = { name: item.name, amount: item.amount }) : (hash[item.name].amount += item.amount), hash), {}));

Addis · Accepted Answer · 2020-01-29 20:11:05Z

2

To give alternative answer using forEach and find:

var userData = [
  {name: "user1", amount: 80},
  {name: "user1", amount: 12},
  {name: "user1", amount: 8},
  {name: "user2", amount: 60},
  {name: "user2", amount: 12},
  {name: "user3", amount: 90},
  {name: "user3", amount: 28}
]

let userGrandTotal = [];

userData.forEach(user => {
  let grandUser = userGrandTotal.find(userGrand => userGrand.name === user.name);
  if(grandUser) {
    grandUser.amount += user.amount;
  }
  else {
    userGrandTotal.push(user)
  }
})

console.log(userGrandTotal)

answered Jan 29, 2020 at 20:11

Addis

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