How to sort object according to nested array elements

Question

I need to sort the main data by the oldest created account. In the example below, the first element in the list would be id = 2. That's because the id = 2 contains the oldest created account (named account3, which was created at 2020-10-05, while the other accounts have been created after that date). I'm using nodejs. Is there an es-function that can solve this problem in an easy way?

The object data looks like this:

{
  "data": [{
    "id": 1,
    "accounts": [{
      "id": 333,
      "data": {
        "name": "account1",
        "createdAt": "2020-10-07T09:27:28.032Z"
      }
    }]
  }, {
    "id": 2,
    "accounts": [{
      "id": 334,
      "data": {
        "name": "account2",
        "createdAt": "2020-10-06T09:27:28.032Z"
      }
    }, {
      "id": 335,
      "data": {
        "name": "account3",
        "createdAt": "2020-10-05T09:27:28.032Z"
      }
    }]
  }]
}

Please take a look at How to Ask and produce a minimal reproducible example of your effort with expected output — mplungjan
– mplungjan, Commented Oct 7, 2020 at 12:50
it would be better if you fetch this data sorted from your database it would be more efficient — Joseph
– Joseph, Commented Oct 7, 2020 at 12:50
Data is in elasticsearch. I wanted to avoid to sort it there because Im afraid I would need to use painless-script to achieve that, which is also quite difficult. — oderfla
– oderfla, Commented Oct 7, 2020 at 12:53

plalx · Accepted Answer · 2020-10-07 13:18:28Z

You can often solve this problem with map --> sort --> map. It does 3 passes on the input but remains O(n log n). You could further optimize, but I doubt this becomes a bottleneck.

Map to [record, oldestAccountDate] tuples.
Sort the tuples by oldestAccountDate.
Map again to unwrap the record.

const wrapper = {
  "data": [{
    "id": 1,
    "accounts": [{
      "id": 333,
      "data": {
        "name": "account1",
        "createdAt": "2020-10-07T09:27:28.032Z"
      }
    }]
  }, {
    "id": 2,
    "accounts": [{
      "id": 334,
      "data": {
        "name": "account2",
        "createdAt": "2020-10-06T09:27:28.032Z"
      }
    }, {
      "id": 335,
      "data": {
        "name": "account3",
        "createdAt": "2020-10-05T09:27:28.032Z"
      }
    }]
  }]
};

wrapper.data = wrapper.data
  .map(rec => [rec, Math.min(...rec.accounts.map(acc => new Date(acc.data.createdAt)))])
  .sort((a, b) => a[1] - b[1])
  .map(tuple => tuple[0]);
  
  
 console.log(wrapper);

secan · Accepted Answer · 2020-10-07 13:32:26Z

1

const data = [{
  "id": 1,
  "accounts": [{
    "id": 333,
    "data": {
      "name": "account1",
      "createdAt": "2020-10-07T09:27:28.032Z"
    }
  }]
}, {
  "id": 2,
  "accounts": [{
    "id": 334,
    "data": {
      "name": "account2",
      "createdAt": "2020-10-06T09:27:28.032Z"
    }
  }, {
    "id": 335,
    "data": {
      "name": "account3",
      "createdAt": "2020-10-05T09:27:28.032Z"
    }
  }]
}]

const sorted = data.sort((a, b) => {
  const aOldestDate = a.accounts.reduce((acc, item) => {
    const itemDate = new Date(item.data.createdAt);
    return itemDate < acc && itemDate || acc;
  }, new Date());
  
  const bOldestDate = b.accounts.reduce((acc, item) => {
    const itemDate = new Date(item.data.createdAt);
    return itemDate < acc && itemDate || acc;
  }, new Date());
  
  return aOldestDate - bOldestDate;
});

console.log(sorted);

answered Oct 7, 2020 at 13:32

secan

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2 Comments

plalx Over a year ago

You can do that but it becomes O(n * n log n) complexity because you re-resolve the oldest account for every compare.

secan Over a year ago

@plalx, thank you very much for your comment. I am a self-thought developer with no formal education in CS; many "theoretical" arguments like algorithms complexity are not (yet) something I am familiar with. That is a topic I'll have to learn sooner rather than later. :)

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