Data Processing in JavaScript

Question

New to JS, I come from Python world so need some help.

I am fetching some data from B.E. that looks something like:

{
  "Airports": {
    "BCN": {
      "Arrivals": [{ "flight": "BIO", "time": "1:00" , "passengers": 10}, { "flight": "VGU", "time" : "2.00","passengers": 20 }, {"flight": "MEX", "time": "3.00", "passengers": 30 } ],
      "Departures": [{ "flight": "BIO", "time": "1:00" }, { "flight": "VGU", "time" : "2.00" }, {"flight": "MEX", "time": "3.00" }]
    },
 
  }
}

I want to pick up Arrival/Departure data per airport and convert it into a list of dictionaries (Key /Value pairs) something that looks like this :

FlightData.Airports.BCN.Arrivals

[
{"0:00":[]},
{"1:00":["flight": BIO, "passengers": 10]},
{"2:00":["flight": VGU, "passengers": 20]},
{"3:00":["flight": MEX, "passengers": 30]},
]

Is there an easy way to do this. This is what I have tried so far:

let arrivalDict = Object.keys(arrivals).reduce(
    (acc: any, k: any) => (
      (acc[arrivals[k]] = [...(acc[arrivals[k]] || []), k]), acc
    ),
    {}
  );

Is it better to use Lodash?

["flight": BIO, "passengers": 10] is not valid JavaScript. [] is for arrays, only objects have key:value pairs. Do you want an array of objects there? — Barmar
– Barmar, Commented Aug 18, 2021 at 15:39
You need to use arrivals[k].time as the key of the result. — Barmar
– Barmar, Commented Aug 18, 2021 at 15:41
It looks like you want results even when no data is in the array matching it (0:00: []), so the array you map over should probably be an array of times, that you then reach into the data to extract arrivals for. — James
– James, Commented Aug 18, 2021 at 15:43
And your sample result is not an object, it's an array of objects. It would make more sense for it to be a single object with the times as keys (which is what your code creates). — Barmar
– Barmar, Commented Aug 18, 2021 at 15:45
@Appy The good news is that your code does create an array of objects. — Barmar
– Barmar, Commented Aug 18, 2021 at 15:47

Barmar · Accepted Answer · 2021-08-18 15:59:07Z

3

Since arrivals is an array, you don't need to use Object.keys(). Just loop over the array values.

I've used a for loop to create a dictionary that has all the hours as keys. Then I use a forEach() loop to push each of the arrivals dictionaries onto the appropriate element.

let arrivals = [{ "flight": "BIO", "time": "1:00" , "passengers": 10}, { "flight": "VGU", "time" : "2.00","passengers": 20 }, {"flight": "MEX", "time": "3.00", "passengers": 30 } ];

// Fill in all hours from 00:00 to 23:00
let arrivals_obj = {};
for (let hour = 0; hour < 24; hour++) {
  arrivals_obj[`${hour}:00`] = [];
}

Object.values(arrivals).forEach(arrival =>
  arrivals_obj[arrival.time.replace('.', ':')].push(arrival)
);

console.log(arrivals_obj)

answered Aug 18, 2021 at 15:59

Barmar

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1 Comment

Ap-Mich Over a year ago

This is a great solution! thank you, this is great learning

James · Accepted Answer · 2021-08-18 15:51:59Z

1

There are a few ways to accomplish this, if you don't mind starting with an array of times consider this approach:

const data = {
  "Airports": {
    "BCN": {
      "Arrivals": [
        { "flight": "BIO", "time": "1:00" , "passengers": 10}, 
        { "flight": "VGU", "time" : "2:00","passengers": 20 }, 
        {"flight": "MEX", "time": "3:00", "passengers": 30 } 
      ],
      "Departures": [
        { "flight": "BIO", "time": "1:00" }, 
        { "flight": "VGU", "time" : "2:00" }, 
        { "flight": "MEX", "time": "3:00" }
      ]
    }
  }
};

const times = ["0:00", "1:00", "2:00", "3:00"];

const result = Object.fromEntries(
  times.map(t => [t, data.Airports.BCN.Arrivals.filter(arr => arr.time === t)])
);

console.log(result);

answered Aug 18, 2021 at 15:51

James

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1 Comment

Ap-Mich Over a year ago

Thank you @James! This fits my use-case perfectly! You are a life saver!

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