Mapping through an array of objects in javascript

Question

i have an array of objects like this:

[{side: Buy, price: 100}, {side: Buy, price: 110}, {side: Sell, price: 200}, {side: Buy, price: 150} ]

Now i want to calculate for this array the total sum of the Buy and Sell side and for each side the average sum of the prices. To be more specific i want my output to be something like this: Buy = 3 AvgPrice for Buy = 120 Sell = 1 AvgPrice for Sell = 200 I'm new to javascript and react so i have some difficulties. Thanks !:)

What have you tried so far? Sounds like you want to use reduce :) — Davin Tryon
– Davin Tryon, Commented Apr 3, 2017 at 10:18

Michael Peyper · Accepted Answer · 2017-04-03 10:39:25Z

2

Probably easiest to just iterate the array and keep a rolling average for each side.

var data = [{side: 'Buy', price: 100}, {side: 'Buy', price: 110}, {side: 'Sell', price: 200}, {side: 'Buy', price: 150} ];

var tally = { Buy: { count: 0, total: 0 }, Sell: { count: 0, total: 0 } };

data.forEach(item => {
    tally[item.side].count = tally[item.side].count + 1;
    tally[item.side].total = tally[item.side].total + item.price;
})

console.log("AvgPrice for Buy = " + (tally.Buy.total / tall.Buy.count) + " Sell = 1 AvgPrice for Sell = " + (tally.Sell.total / tall.Sell.count));

answered Apr 3, 2017 at 10:39

Michael Peyper

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6 Comments

RamAlx Over a year ago

I think this is the most understandable solution

kind user Over a year ago

Just to clarify, you are hard coding the whole tally variable. What if there would be much more than just Buy and Sell elements? You would just write them down by hand? Unfortunately it won't work effectively, but I agree, now it's much more readable because of less code.

Michael Peyper Over a year ago

@Kinduser There is no point making super dynamic code when the requirements don't call for it. When it comes to buying and selling, there aren't likely to be too many more sides that need to be added, so hard coding them makes sense for future maintainability. Your example will work too, but will take someone a while to understand if they come back to it in a years time (or if a new developer starts on the project).

kind user Over a year ago

@MichaelPeyper It's not that complicated as it seems to be. I'm also just a beginner, which 5 months of experience. Anyways - I just think that when someone is deciding to make a question on so, he is expecting a high quality solution and even if he doesn't understand it - it's a motivation to keep learning.

Michael Peyper Over a year ago

@Kinduser each to his own. I'll take readability over catering for non-existent requirements any day of the week. Also, it wouldn't take much to dynamically generate the tally object if such a requirement ever came about.

|

kind user · Accepted Answer · 2017-04-03 12:29:14Z

1

Simple solution using Array#forEach and Object.keys().

var arr = [{side: 'Buy', price: 100}, {side: 'Buy', price: 110}, {side: 'Sell', price: 200}, {side: 'Buy', price: 150}], obj = {}, res = [];

arr.forEach(function(v){
 (obj[v.side] || (obj[v.side] = [])).push(v.price);
});
var res = Object.keys(obj).reduce(function(s,a) {
  s[a] = obj[a].length;
  s['avg' + a] = obj[a].reduce((a,b) => a + b) / obj[a].length;
  return s;
}, {});
console.log(res);

edited Apr 3, 2017 at 12:29

answered Apr 3, 2017 at 10:32

kind user

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7 Comments

RamAlx Over a year ago

Can we add the output values in a single object? Great answer btw

RamAlx Over a year ago

Like obj = {aSide: 4, bSide: 8, aPrice: 123, bPrice: 12}

kind user Over a year ago

@user7334203 I will try

RamAlx Over a year ago

Sorry for confusing you. is it too complex?

RamAlx Over a year ago

Awesome! Thanks a lot

|

Mayank Shukla · Accepted Answer · 2017-04-03 10:35:09Z

1

Use any iterator like forEach, for etc to iterate the data, and use two object variables, one will store the buy data and other will store sell data.

Write it like this:

var data = [{side: 'Buy', price: 100}, {side: 'Buy', price: 110}, {side: 'Sell', price: 200}, {side: 'Buy', price: 150} ];

var buy = {}, sell = {};

data.forEach(el => {
    if(el.side == 'Buy'){
          buy['count'] = (buy['count'] || 0) + 1;
          buy['total'] = (buy['total'] || 0) + el.price; 
    }else{
         sell['count'] = (sell['count'] || 0) + 1;
         sell['total'] = (sell['total'] || 0) + el.price; 
    }
})

console.log(buy.total/buy.count, sell.total/sell.count);

edited Apr 3, 2017 at 10:35

answered Apr 3, 2017 at 10:29

Mayank Shukla

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Comments

anis programmer · Accepted Answer · 2017-04-03 10:36:56Z

1

Please check this:

    var arrayBuySell=[{side: Buy, price: 100}, {side: Buy, price: 110}, {side: Sell, price: 200}, {side: Buy, price: 150} ]
var averageBuy = 0;
var averageSell = 0;
var totalbuy=0;
var totalbuycount=0;
var totalsellcount=0;
var totalsell=0;
for (var i = 0; i < arrayBuySell.length; i++) {
    if(arrayBuySell[i]="Buy")
      {
       totalbuy+=arrayBuySell[i].price;
       totalbuycount=arrayBuySell[i].price.Count();
      }
     else
      {
       totalsell+=arrayBuySell[i].price;
       totalsellcount=arrayBuySell[i].price.Count();
      }
  }
averageBuy =totalbuy/totalbuycount;
averageSell=totalsell/totalsellcount;

answered Apr 3, 2017 at 10:36

anis programmer

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Comments

Raskolnikov · Accepted Answer · 2017-04-03 10:48:11Z

0

You can do it like this:

let arr = [{side: "Buy", price: 100}, {side: "Buy", price: 110}, {side:     "Sell", price: 200}, {side: "Buy", price: 150} ];
let buyPrices = [];
let sellPrices = [];
arr.forEach((item, index) => {
  if (item.side === 'Buy') {
    buyPrices.push(item.price);
  } else if (item.side === 'Sell') {
    sellPrices.push(item.price);
  }
});

let avgBuy = buyPrices.reduce((a, b) => a + b)/buyPrices.length;
console.log(`Buy -> ${buyPrices.length}
AvgBuyPrices -> ${avgBuy}`);
let avgSell = sellPrices.reduce((a, b) => a + b)/sellPrices.length;
console.log(`Sell -> ${sellPrices.length}
AvgSellPrices -> ${avgSell}`);

answered Apr 3, 2017 at 10:48

Raskolnikov

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