Count array inside array of object

Question

Suppose I have an array of Object as:

Expected O/P : {alpha:4, beta:8}

For this I tried as:

const apple = [{
    name: 'alpha',
    details: [{
      "attachment": [123, 456]
    }, {
      "attachment": [1454, 1992]
    }]
  },
  {
    name: 'beta',
    details: [{
      "attachment": ["12", 189]
    }, {
      "attachment": ["maggi", 1890, 2000]
    }, {
      "attachment": [1990, 2001, 2901]
    }]
  }
];

const appleDetails = [];

for (let i = 0; i < apple.length; i++) {
  for (let j = 0; j < apple[i].details.length; j++) {
    const {
      name
    } = apple[i];
    const {
      attachment
    } = apple[i].details[j]
    appleDetails.push({
      name,
      attachment
    })
  }
}

let appleData = [];
appleDetails.forEach(({
  name,
  attachment
}) => {
  attachment.forEach((attatchId) => {
    appleData.push({
      name,
      _id: attatchId
    })
  })
})

const eachAppleCount = appleData.reduce((acc, item) => {
  const key = item.name
  if (!acc.hasOwnProperty(key)) {
    acc[key] = 0
  }
  acc[key] += 1
  return acc
}, {})

console.log(eachAppleCount);

This gives the O/P as required i.e. : {alpha:4, beta:8}

But the process involved is too much, is there any more efficient way such that,by using:

const apple = [{
    name: 'alpha',
    details: [{
        "attachment": [123, 456]
    }, {
        "attachment": [1454, 1992]
    }]
}, {
    name: 'beta',
    details: [{
        "attachment": ["12", 189]
    }, {
        "attachment": ["maggi", 1890, 2000]
    }, {
        "attachment": [1990, 2001, 2901]
    }]
}];

We can count the value for each apple name. If anyone needs any further information please do let me know.

Siva Pradhan did u see answer below?

Lior Kaminsky
– Lior Kaminsky

2021-04-19 19:01:15 +00:00
Commented Apr 19, 2021 at 19:01 — Lior Kaminsky
– Lior Kaminsky, Commented Apr 19, 2021 at 19:01

AbsoluteBeginner · Accepted Answer · 2021-04-19 13:48:36Z

3

This will do the work

const apple = [{
  name: 'alpha',
  details: [{
    "attachment": [123, 456]
  }, {
    "attachment": [1454, 1992]
  }]
}, {
  name: 'beta',
  details: [{
    "attachment": ["12", 189]
  }, {
    "attachment": ["maggi", 1890, 2000]
  }, {
    "attachment": [1990, 2001, 2901]
  }]
}];

const result = apple.reduce((acc, curr) => {
  if (acc[curr.name] === undefined) acc[curr.name] = 0;
  curr.details.forEach((d) => (acc[curr.name] += d.attachment.length));
  return acc;
}, {});

console.log(result);

edited Apr 19, 2021 at 13:48

AbsoluteBeginner

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answered Apr 19, 2021 at 13:12

Lior Kaminsky

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1 Comment

Siva Pradhan Over a year ago

It worked perfectly. Thank you so much. :)

Karan · Accepted Answer · 2021-04-20 04:08:01Z

-1

Try like below.

Array.prototype.map() - The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.
Create new object as {[a.name]: values} where we use [a.name] inside [] so value from a.name will be set as object key.
To get value we use Array.prototype.flatMap() - The flatMap() method returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level.
Get all attachments with a.details.flatMap(d => d.attachment) and use .length to get total count as value.
map will return result in format of array of objects.
Use Array.prototype.reduce() with spread syntax (...) to club array of objects into single object.

const apple = [
               { name: 'alpha', details: [{"attachment": [ 123, 456 ]}, {"attachment": [1454, 1992 ]} ]},
               {name: 'beta', details: [{"attachment": [ "12", 189 ]},{"attachment": ["maggi", 1890,2000 ]}, {"attachment": [1990, 2001,2901 ]} ]}
              ];

// map will return result in format of array of objects
let resultArr = apple.map(a => ({[a.name]: a.details.flatMap(d => d.attachment).length }));

// use reduce with spread syntax (...) to club array of objects into single object.
let result = resultArr.reduce((i, a) => ({...a, ...i}), {});

console.log(result);

edited Apr 20, 2021 at 4:08

answered Apr 19, 2021 at 13:20

Karan

12.7k3 gold badges31 silver badges45 bronze badges

5 Comments

Lior Kaminsky Over a year ago

for the below input your answer won't be unique per apple name (u will have 2 entries of alpha apple which i believe is not good):

const apple = [   { name: 'alpha', details: [{ attachment: [123, 456] }, { attachment: [1454, 1992] }] },   { name: 'alpha', details: [{ attachment: [123, 456, 222] }, { attachment: [1454, 1992] }] },   {     name: 'beta',     details: [       { attachment: ['12', 189] },       { attachment: ['maggi', 1890, 2000] },       { attachment: [1990, 2001, 2901] },       { attachment: [1990, 2001, 2901] },     ],   }, ];

Karan Over a year ago

@LiorKaminsky, Yes, you are correct. If in case of OP can have multiple entries for alpha then he should better go with solution that you have provided.

VLAZ Over a year ago

The output seems different to what OP expects. This will create an object for each sum and return an array. OP expects a single object with the names as key and the count as values.

Karan Over a year ago

@VLAZ, thanks for pointing that out. Updated answer.

VLAZ Over a year ago

I'm personally not a big fan of continually spreading objects with reduce(). I'd probably go for making resultArr an array of pairs, then just use Object.fromEntries() on it: jsbin.com/kinayot/edit?js,console Another alternative is with your current code to call resultArr.reduce((i, a) => Object.assign(i, a), {})

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