Group js objects by multiple properties

Question

In the example below I have an array of objects which I group by 2 of their properties (based on https://stackoverflow.com/a/40142591).

        var arr = [{
            


        

Answer 1

I believe the below kind of grouping should solve the problem:

var arr=[{id:1,tags:"main",yearCode:"2018"},{id:2,tags:["main","blue"],yearCode:"2018"},{id:3,tags:["main","green"],yearCode:"2018"},{id:25,tags:["green"],yearCode:"2018"},{id:26,tags:["important"],yearCode:"2017"},{id:29,tags:["important","blue"],yearCode:"2017"},{id:2,tags:["important","green"],yearCode:"2017"}];

var mainFilter = "yearCode";
var secFilter = "tags";

var result = arr.reduce((map, obj) => {

    if (!map[obj[mainFilter]]) map[obj[mainFilter]] = {};

    [].concat(obj[secFilter]).forEach(subEl => {

        if (!map[obj[mainFilter]][subEl]) map[obj[mainFilter]][subEl] = [];

        map[obj[mainFilter]][subEl].push(obj);

    });

    return map;

}, {});

console.log(result);