How to convert array of objects to object of array in javascript?

Question

I am trying to convert array of objects to object of array using javascript.

Here is the code

const data = [{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "16",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma12313"
},
 {
 yearMonthKey: "201908",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
}]
let programs = {};

I want to use programs object to make an object out of it like this below.

{
 201907: {
 15: [{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
 },
 {
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma123132"
 }],
 16: [{
 yearMonthKey: "201907",
 dayKey: "16",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
 }]
 },
 201908: {
 15: [{
 yearMonthKey: "201908",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
 }]
 }
}

I try to solve it using map in array method.

data.map(item => {
 programs[item.yearMonthKey] : {
 programs[item.dayKey] : [{
 }]
 }
})

but it is bit challenging to sort objects as a value of same dayKey key inside of an array and put those inside of same yearMonthKey.

• Ele: You can't use the function map when the desired result is a key-value object

Answer 1

You could reduce the array. Add each yearMonthKey to the accumulator. Based on the yearMonthKey add a nested dayKey key to the acc[yearMonthKey] object and default it to an array.

const data=[{yearMonthKey:"201907",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"},{yearMonthKey:"201907",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"},{yearMonthKey:"201907",dayKey:"16",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma12313"},{yearMonthKey:"201908",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"}];
const output = data.reduce((acc, o) => {
 if (!acc[o.yearMonthKey]) 
 acc[o.yearMonthKey] = {};
 
 if (!acc[o.yearMonthKey][o.dayKey]) 
 acc[o.yearMonthKey][o.dayKey] = [];
 
 acc[o.yearMonthKey][o.dayKey].push(o);
 
 return acc;
}, {})
console.log(output)

Answer 2

const data = [{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "16",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma12313"
},
 {
 yearMonthKey: "201908",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
}]
let programs = {};
data.forEach(function(element) {
 if (typeof programs[element.yearMonthKey] == "undefined") {
 programs[element.yearMonthKey] = {};
 }
 
 if(typeof programs[element.yearMonthKey][element.dayKey] == "undefined") {
 programs[element.yearMonthKey][element.dayKey] = [];
 }
 
 programs[element.yearMonthKey][element.dayKey].push(
 element
 );
});
console.log(programs);

Answer 3

Universal function for grouping with any keys

function group() {
 const args = Array.from(arguments)
 const data = args.shift()
 const result = {}
 data.forEach(elem => {
 let level = result
 args.forEach((groupProp, ind) => {
 const groupValue = elem[groupProp]
 if (groupValue in level) {
 level = level[groupValue]
 } else {
 level = level[groupValue] = ind === args.length - 1 ? [] : {}
 }
 })
 level.push(elem)
 })
 return result 
}
const data = [{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "16",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma12313"
},
 {
 yearMonthKey: "201908",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
}]
const result = group(data, 'yearMonthKey', 'dayKey')
console.log(result)

Answer 4

const data=[{yearMonthKey:"201907",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"},{yearMonthKey:"201907",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"},{yearMonthKey:"201907",dayKey:"16",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma12313"},{yearMonthKey:"201908",dayKey:"15",startDate:"2019-07-15 00:00:00+0900",title:"testProgrma"}];
const dist_yearMonthKeys = [...new Set(data.map(d => d.yearMonthKey))];
let program = {};
for (let ymk of dist_yearMonthKeys) {
 const ymk_num = parseInt(ymk); // error-prone, be careful with your source data
 program[ymk_num] = {};
 const dist_dayKeys = [...new Set(data.filter(d => d.yearMonthKey === ymk).map(d => d.dayKey))];
 for (let dk of dist_dayKeys) {
 const dk_num = parseInt(dk); // error-prone
 program[ymk_num][dk_num] = data.filter(d => d.dayKey === dk && d.yearMonthKey === ymk);
 }
}
console.log(program);

This gives numeric keys, like you requested.

• adiga: There is no point in doing parseInt(ymk). Keys of an object are either a string or a Symbol. When you add program[ymk_num] it will be converted to a string.

Answer 5

try destructuring the list and putting it back together in the format you want

const data = [{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
},
 {
 yearMonthKey: "201907",
 dayKey: "16",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma12313"
},
 {
 yearMonthKey: "201908",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
}]
const [1,2,3,4] = data

so now when you call variable 1 you would get

{
 yearMonthKey: "201907",
 dayKey: "15",
 startDate: "2019-07-15 00:00:00+0900",
 title: "testProgrma"
} 

Now you can handle each object individually instead of in a list. As such you can basically do whatever you want with the objects