Adding values from objects in an array

Question

I have an array of objects:

var array = [{
    id: "cards",
    amount: 5
}, {
    id: "shirts",
    amount: 3
}, {
    id: "cards",
    amount: 2
}, {
    id: "shirts",
    amount: 3
}]

What I need to do is loop through this array and find the total of all id types. So in this example, I would find the total amount of cards and shirts.

I'm not sure how to do this with objects. I've tried stripping the objects down with Object.values(array), but is there a way to do it with the objects?

Thanks for your help.

cyr_x · Accepted Answer · 2017-02-23 17:56:52Z

1

This should do what you want:

var array = [
  { id: "cards", amount: 5 }, 
  { id: "shirts", amount: 3 },
  { id: "cards", amount: 2 }, 
  { id: "shirts", amount: 3 }
];

var result = array.reduce(function(entities, item) {
       entities[item.id] = (entities[item.id] || 0) + item.amount;
       return entities;
}, {})


console.log(result);

edited Feb 23, 2017 at 17:56

answered Feb 23, 2017 at 17:23

cyr_x

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Comments

marchWest · Accepted Answer · 2017-02-23 17:16:39Z

1

You would loop your array, check the id property for your target object, then enumerate and outer scope variable with the value stored in the amount property.

var totalShirts = 0;
var totalCards = 0;
for(var i = 0, len = array.length; i < len; i++){
    var entry = array[i];
    if(entry.id === "cards"){
        totalCards += entry.amount;
    }
    else if(entry.id === "shirts"){
        totalShirts += entry.amount;
    }
}
console.log("Total Cards: " + totalCards);
console.log("Total Shirts: " + totalShirts);

answered Feb 23, 2017 at 17:16

marchWest

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Comments

Ionut · Accepted Answer · 2017-02-23 17:23:01Z

1

Here is an example that gets the total of each item

var array = [{id:"cards", amount: 5}, {id:"shirts", amount: 3}, {id:"cards", amount: 2}, {id:"shirts", amount: 3}];

var result = array.reduce(function(accumulator, current) {
  if (!(current.id in accumulator)) {
    accumulator[current.id] = current.amount;
  } else {
    accumulator[current.id] += current.amount;
  }
  
  return accumulator;
}, {});

console.log(result);

answered Feb 23, 2017 at 17:23

Ionut

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Comments

Ronan · Accepted Answer · 2017-02-24 14:02:09Z

1

A simple forEach will do the trick:

var counts = {}
array.forEach(v => {
  counts[v.id] = (counts[v.id] || 0) + v.amount
})
console.log(counts)

will print:

{
    cards: 7
    shirts: 6
}

edited Feb 24, 2017 at 14:02

answered Feb 23, 2017 at 17:27

Ronan

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4 Comments

guest271314 Over a year ago

Is return statement necessary?

HappyGreybush Over a year ago

@guest271314 - I assume so because the return will add the new count to the counts object...?

guest271314 Over a year ago

@HappyGreybush return statement can be omitted. counts[v.id] = (counts[v.id] || 0) + v.amount assigns the value.

Ronan Over a year ago

Indeed, return is not necessary, I had a solution using .map that I changed for a forEach and forgot about that :) Edited

vinoth h · Accepted Answer · 2017-02-23 17:18:56Z

0

Here is a O(n) time solution.

var totals = new Object();

for(var i = 0;i < array.length;i ++) {
  var id = array[i].id;
  var amount = array[i].amount;
  if(totals[id] == undefined) {
    totals[id] = amount; 
  } else {
    totals[id] += amount;
  }
}
console.log(totals);

answered Feb 23, 2017 at 17:18

vinoth h

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Comments

guest271314 · Accepted Answer · 2017-02-23 17:20:13Z

0

You can use for..of loop

var array = [{
  id: "cards",
  amount: 5
}, {
  id: "shirts",
  amount: 3
}, {
  id: "cards",
  amount: 2
}, {
  id: "shirts",
  amount: 3
}]

let res = {};

for (let {id,amount} of array) {
  if (!res.hasOwnProperty(id)) res[id] = 0;
  res[id] += amount;
}

console.log(res);

answered Feb 23, 2017 at 17:20

guest271314

1

Comments

Luis Alves · Accepted Answer · 2017-02-23 17:20:48Z

0

Use a for-loop to do this:

var totalCards = 0; 
var totalShirt = 0;
for (var i = 0; i < arr.length; i++) {
    if (arr[i].id === "cards") {
        totalCards += arr[i].amount;
    } else {
        totalShirt += arr[i].amount;
    }
}

answered Feb 23, 2017 at 17:20

Luis Alves

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Comments

Workion · Accepted Answer · 2017-02-23 17:21:08Z

0

Do the magic in for loop. This example should be general enough:

var array = [ {id:"cards", amount: 5}, {id:"shirts", amount: 3}, {id:"cards", amount: 2}, {id:"shirts", amount: 3} ];
var output = [];
    
for(var i of array) {
  if(!output[i.id]) {
    output[i.id] = 0;
  }
  output[i.id] += i.amount;
}
    
console.log(output);

answered Feb 23, 2017 at 17:21

Workion

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Comments

kind user · Accepted Answer · 2017-02-23 17:24:52Z

0

var array = [{id:"cards", amount: 5}, {id:"shirts", amount: 3}, {id:"cards", amount: 2}, {id:"shirts", amount: 3}];

var arr = [];
array.forEach(v => arr.push(v.id));
var newArr = [...new Set(arr)];
var arr2 = [];

newArr.forEach(function(v) {
  var obj = {};
  obj.id = v;
  obj.counter = 0;
  arr2.push(obj);
});

arr2.forEach(v => array.forEach(c => c.id == v.id ? v.counter += c.amount : v));
console.log(arr2);

answered Feb 23, 2017 at 17:24

kind user

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Comments

Dan Nagle · Accepted Answer · 2017-02-23 17:29:11Z

0

You can use Array.forEach() to iterate over each element of the array. The total object is an associative array where the index is the id field of array element objects.

var array = [{ id: "cards", amount: 5 },
             { id: "shirts", amount: 3 },
             { id: "cards", amount: 2},
             { id: "shirts", amount: 3 }];
var total = {};
array.forEach(function (el) {
  if (total[el.id]) {
    total[el.id] += el.amount
  } else {
    total[el.id] = el.amount
  }
});
console.log(JSON.stringify(total));

answered Feb 23, 2017 at 17:29

Dan Nagle

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Comments

Nina Scholz · Accepted Answer · 2017-02-23 17:49:52Z

0

You could use Array#reduce and sum the amount.

var array = [{ id: "cards", amount: 5 }, { id: "shirts", amount: 3 }, { id: "cards", amount: 2 }, { id: "shirts", amount: 3 }],
    result = array.reduce(function (r, a) {
        r[a.id] = (r[a.id] || 0) + a.amount;
        return r;
    }, {});
    
console.log(result);

edited Feb 23, 2017 at 17:49

answered Feb 23, 2017 at 17:18

Nina Scholz

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3 Comments

kind user Over a year ago

I'm afraid that he wants total amount of each types, not just total amount of everything.

Nina Scholz Over a year ago

@Kinduser, i was thinking i was missing something.

Nina Scholz Over a year ago

@Kinduser i am so delighted ;-)

Manish Jakhmola · Accepted Answer · 2017-02-23 17:36:47Z

-1

You can use this code

if (!Object.keys) {
    Object.keys = function (obj) {
        var keys = [],
            k;
        for (k in obj) {
            if (Object.prototype.hasOwnProperty.call(obj, k)) {
                keys.push(k);
            }
        }
        return keys;
    };
}

then you can do this in older browsers as well:

var len = Object.keys(obj).length;

answered Feb 23, 2017 at 17:36

Manish Jakhmola

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