Transpose data in array of objects

Question

I have following data and want to transpose with the revenue as the value of individual years:

Current data:

[{"year": 2017, "month": "Jan", "revenue": 2000},
{"year": 2017, "month": "Feb", "revenue": 3000},
{"year": 2017, "month": "Mar", "revenue": 1000},
{"year": 2016, "month": "Jan", "revenue": 5000}, 
{"year": 2016, "month": "Feb", "revenue": 4000}, 
{"year": 2016, "month": "Mar" "revenue": 2000}]

Expected output:

[{Month: "Jan", "2017": 2000, "2016": 5000},
{Month: "Feb", "2017": 3000, "2016": 4000},
{Month: "Mar", "2017": 1000, "2016": 2000}]

I've been trying different ways but no success. Also in future I might have months different than Jan-Mar so any solution which isn't restricted to three months.

• Muhammad Usman: I've been trying different ways but no success you should post that code too
• Luca Kiebel: Please add the way you tried that got you the closest to what you want as a minimal reproducible example
• Jonathan Lonowski: This may help you get started: What is the most efficient method to groupby on a JavaScript array of objects?

Answer 1

A basic plan is to make a new object keyed to the month and add each year as you go through. reduce() makes it pretty concise:

let dates = [
 {"year": 2017, "month": "Jan", "revenue": 2000},
 {"year": 2017, "month": "Feb", "revenue": 3000},
 {"year": 2017, "month": "Mar", "revenue": 1000},
 {"year": 2016, "month": "Jan", "revenue": 5000},
 {"year": 2016, "month": "Feb", "revenue": 4000},
 {"year": 2016, "month": "Mar", "revenue": 2000}
]
// You only want an array of values, so just return Object.values()
let d = Object.values(dates.reduce((a, c) =>{
 // either use the existing entry or create a new one
 // with month already set
 (a[c.month] || (a[c.month] = {Month: c.month}))[c.year] = c.revenue;
 return a;
}, {}))
console.log(d)

:

• Hannan: Thanx a lot. Apart from accepting it as accepted answer, I wish I could also give u a hug :)

Answer 2

You can use ES6 syntax Array.reduce to build up your array using the data you have.

const values = [{
 year: 2017,
 month: "Jan",
 revenue: 2000,
 },
 {
 year: 2017,
 month: "Feb",
 revenue: 3000,
 },
 {
 year: 2017,
 month: "Mar",
 revenue: 1000,
 },
 {
 year: 2016,
 month: "Jan",
 revenue: 5000,
 },
 {
 year: 2016,
 month: "Feb",
 revenue: 4000,
 },
 {
 year: 2016,
 month: "Mar",
 revenue: 2000,
 }
];
// Use destructuration to access each data
const transformedValues = values.reduce((tmp, {
 month,
 year,
 revenue,
}) => {
 // Look for the month in tmp
 const monthInTmp = tmp.find(y => y.Month === month);
 // If it do not exist, push it
 if (!monthInTmp) {
 tmp.push({
 Month: month,
 // use the following syntax [var] to use a dynamical key
 [year]: revenue,
 });
 return tmp;
 }
 // if it exists update it
 // handle the case when we have two revenue in same year
 if (monthInTmp[year]) {
 monthInTmp[year] += revenue;
 
 return tmp;
 }
 
 monthInTmp[year] = revenue;
 return tmp;
}, []);
console.log(transformedValues );