How can I loop through an Object of Objects and an Array of Objects and update nested object values based on the count of matching array elements?

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Let's say I have some data organized like so...

dataArr = [
    {service: s1, status: ready},
    {service: s2, status: ready},
    {service: s1, status: retired},
    {service: s3, status: retired},
    {service: s2, status: ready}
]

There are 3 distinct services. Each data element has one of the three service types, and has a status of either retired or ready.

How can I loop through each element in the dataArr to create the following statusByServiceObj? For instance, within all the data, I want to find all s1 service types, and then determine how many s1's are in a retired or ready state.

statusByServiceObj = {
    {s1: {ready: 1, retired: 1} },
    {s2: {ready: 2, retired: 0} },
    {s3: {ready: 0, retired: 1} },
}

Where I am currently, I have looped through the dataArr array to create an object like so:

let obj = {};
let nestedObj = {};

dataArr.forEach(ele => {
    obj[ele.service] = nestedObj;
    nestedObj[ele.status] = 0;
});

// obj now equals...
obj = {
    {s1: {ready: 0, retired: 0} },
    {s2: {ready: 0, retired: 0} },
    {s3: {ready: 0, retired: 0} },
}

I'm struggling to populate the ready and retired counts based on service type, when looping through my dataArr.

Very open to best practice recommendations, new to JS. I feel like I'm going braindead when applying the 0 value... should be a count of sorts. Or possibly converting the Object of Objects to an Array of Objects...

I attemted to count the status values by services like so:

dataArr.forEach(ele => {
    for (let service in obj) {
        let countsObj = obj[service];
        for (let status in countsObj) {
            if (ele.service === service && ele.status === status) {
                countsObj[status = countsObj[status] + 1;
            }
        }
    }
}

However, this returns on obj that's getting the total counts of each status in the entire dataArr, ready or retired, and applies it to each service object:

obj = {
    {s1: {ready: 3, retired: 2} },
    {s2: {ready: 3, retired: 2} },
    {s3: {ready: 3, retired: 2} },
}
data-structures reduce arrays javascript
1 Answers

You can use reduce to achieve the desired result

const dataArr = [
  { service: "s1", status: "ready" },
  { service: "s2", status: "ready" },
  { service: "s1", status: "retired" },
  { service: "s3", status: "retired" },
  { service: "s2", status: "ready" },
];

const result = dataArr.reduce((acc, curr) => {
  const { service, status } = curr;
  if (!acc[service]) acc[service] = { ready: 0, retired: 0 };
  acc[service][status] += 1;
  return acc;
}, {});

console.log(result);
/* This is not a part of answer. It is just to give the output fill height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

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