Transform flat array of objects into nested objects

Question

I have an array of task objects and I want to transform these into a multidimensional object grouped by ownerID

var tasks = [ 
{taskID: "1", title: "task1", ownerID: "100", ownerName: "John", allocation: 80}, 
{taskID: "2", title: "task2", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
{taskID: "3", title: "task3", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
{taskID: "4", title: "task4", ownerID: "120", ownerName: "Mike", allocation: 25},
{taskID: "5", title: "task5", ownerID: "120", ownerName: "Mike", allocation: 45}];

This is my expected output:

var people = {
 100: { ownerName: "John", 
 tasks: { 
 {taskID: "1", title: "task1", allocation: 80}
 } 
 },
 110: { ownerName: "Sarah", 
 tasks: { 
 {taskID: "2", title: "task2", allocation: 50}
 {taskID: "3", title: "task3", allocation: 50}
 } 
 },
 120: { ownerName: "Mike", 
 tasks: { 
 {taskID: "4", title: "task4", allocation: 25}
 {taskID: "5", title: "task5", allocation: 45}
 } 
 },
 };

I'm looping through the original data and assigning each row

people[ownerID] = {};
person = people[ownerID];
person['ownerName'] = ownerName;
person['tasks'] = {};
person[taskID] = {};
task = person[taskId];
task['taskID'] = taskID;

This seems to group by ownerID fine and creates a nested object of tasks but it will only add one task for each person.

Argh. Any help really appreciated.

• Nina Scholz: tasks should be an array, not an object.
• ginsberg: @NinaScholz why? would I still be able to access individual tasks using people[100].tasks[3].title if they were an array?
• Nina Scholz: i was wondering, which data type you are using. the above is not a valid example. if you need properties, which reflects the taskID, then you need to use it in the example as well.

Answer 1

Here is a functional way to do it (assuming ownerName is functional dependent on ownerID):

const tasks = [ 
 {taskID: "1", title: "task1", ownerID: "100", ownerName: "John", allocation: 80}, 
 {taskID: "2", title: "task2", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
 {taskID: "3", title: "task3", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
 {taskID: "4", title: "task4", ownerID: "120", ownerName: "Mike", allocation: 25},
 {taskID: "5", title: "task5", ownerID: "120", ownerName: "Mike", allocation: 45}];
const result = tasks.reduce( (acc, {taskID, title, ownerID, ownerName, allocation }) => {
 (acc[ownerID] = acc[ownerID] || { ownerName, tasks: [] })
 .tasks.push( { taskID, title, allocation } );
 return acc;
}, {});
console.log(result);

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• Dan Zuzevich: Nice it works. Is there anyway you could provide some explanation to what you mean as functional dependent? I am actually just getting started with functional programming.
• trincot: ownerName is functional dependent on ownerID when it is always true that given a value for ownerID, there can be only one value for ownerName associated with it, never two.
• Dan Zuzevich: Nice, I like it.

Answer 2

people[ownerID] = {};
person['tasks'] = {};

These lines don't check if an object with the same key exists before and create a new object each time.

Try changing it to

people[ownerID] = people[ownerID] || {};
person['tasks'] = person['tasks'] || {};

• ginsberg: Amazing. So simple. Thank you.

Answer 3

Just one thing, the tasks should be an array, since objects can't hold another objects without having a key.

var tasks = [ 
{taskID: "1", title: "task1", ownerID: "100", ownerName: "John", allocation: 80}, 
{taskID: "2", title: "task2", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
{taskID: "3", title: "task3", ownerID: "110", ownerName: "Sarah", allocation: 50}, 
{taskID: "4", title: "task4", ownerID: "120", ownerName: "Mike", allocation: 25},
{taskID: "5", title: "task5", ownerID: "120", ownerName: "Mike", allocation: 45}];
var transformed = tasks.reduce((obj, item)=> {
 if(!obj[item.ownerID]) {
 obj[item.ownerID] = {};
 }
 obj[item.ownerID].ownerName = item.ownerName;
 if(!obj[item.ownerID].tasks) {
 obj[item.ownerID].tasks = [];
 }
 obj[item.ownerID].tasks.push({taskID: item.taskID, title: item.title, allocation: item.allocation})
 return obj;
}, {})
console.log(transformed);

Answer 4

You could use the logical OR as default operator ans assign a new object if the peroperty does not exists.

var tasks = [{ taskID: "1", title: "task1", ownerID: "100", ownerName: "John", allocation: 80 }, { taskID: "2", title: "task2", ownerID: "110", ownerName: "Sarah", allocation: 50 }, { taskID: "3", title: "task3", ownerID: "110", ownerName: "Sarah", allocation: 50 }, { taskID: "4", title: "task4", ownerID: "120", ownerName: "Mike", allocation: 25 }, { taskID: "5", title: "task5", ownerID: "120", ownerName: "Mike", allocation: 45 }],
 people = {};
tasks.forEach(({ taskID, title, ownerID, ownerName, allocation }) => {
 people[ownerID] = people[ownerID] || { ownerName, tasks: {} };
 people[ownerID].tasks[taskID] = people[ownerID].tasks[taskID] || { taskID, title, allocation };
});
console.log(people);

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