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?

• Barmar: ["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: You need to use arrivals[k].time as the key of the result.
• James: 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.
• Barmar: 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: @Appy The good news is that your code does create an array of objects.

Answer 1

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)

• Ap-Mich: This is a great solution! thank you, this is great learning

Answer 2

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);

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