Turn array of objects into array of unique combinations of its properties

Question

I have to extract specific data from an object. My code works but I wonder if I could improve it by using method like map or filter.

This is for no specific background just for personnel training. Also I am using Lodash library

function extractApi(data) {

  var arrayOfTowns = [];
  var arrayOfCityCode = [];
  var result = [];

//looping throw the expected datas (cities and postcode)
  for (var i = 0; i < data.features.length; i++) {
    arrayOfCityCode.push(_.toString(data.features[i].properties.postcode));
    arrayOfTowns.push(_.toString(data.features[i].properties.city));

//verify unique cities
    arrayOfTowns = _.uniq(arrayOfTowns);

//pushing to a new array to have the expected result format
    if (arrayOfTowns[i] != undefined && arrayOfCityCode != undefined){
      result[i] = arrayOfCityCode[i] + " " + arrayOfTowns[i]
    }      
  }

  return result

}

//example with some datas
extractApi(  {
      "type": "FeatureCollection",
      "limit": 20,
      "version": "draft",
      "licence": "ODbL 1.0",
      "attribution": "BAN",
      "features": [
        {
          "type": "Feature",
          "properties": {
            "importance": 0.6466,
            "type": "municipality",
            "adm_weight": 4,
            "postcode": "43000",
            "context": "43, Haute-Loire, Auvergne-Rhône-Alpes (Auvergne)",
            "id": "43157",
            "population": 18.8,
            "x": 769600,
            "y": 6438600,
            "name": "Le Puy-en-Velay",
            "citycode": "43157",
            "label": "Le Puy-en-Velay",
            "city": "Le Puy-en-Velay",
            "score": 0.8769636363636364
          },
          "geometry": {
            "coordinates": [
              3.883955,
              45.043141
            ],
            "type": "Point"
          }
        },
        {
          "type": "Feature",
          "properties": {
            "importance": 0.0867,
            "type": "municipality",
            "adm_weight": 1,
            "postcode": "43000",
            "context": "43, Haute-Loire, Auvergne-Rhône-Alpes (Auvergne)",
            "id": "43089",
            "population": 3.6,
            "x": 767600,
            "y": 6438900,
            "name": "Espaly-Saint-Marcel",
            "citycode": "43089",
            "label": "Espaly-Saint-Marcel",
            "city": "Espaly-Saint-Marcel",
            "score": 0.8260636363636362
          },
          "geometry": {
            "coordinates": [
              3.858597,
              45.046041
            ],
            "type": "Point"
          }
        },
      ],
      "query": "43000"
    }

 )

The goal is to receive all data.features.properties.postcode and data.features.properties.city and push it to an array. For this example the expected result is ["43000 Le Puy-en-Velay", "43000 Espaly-Saint-Marcel"]. Cities in the result should be unique.

Your code throws an error Uncaught ReferenceError: _ is not defined — Yevhen Horbunkov
– Yevhen Horbunkov, Commented Jul 23, 2019 at 8:10
this is because i use lodash librairy, you can test it here lodash.com/docs/4.17.14 — maxd
– maxd, Commented Jul 23, 2019 at 8:27

nbokmans · Accepted Answer · 2019-07-23 08:36:31Z

2

You can indeed use .map to get the results you desire:

const parsedCities = data.features
    .map(f => `${f.properties.postcode} ${f.properties.city}`)
    .filter((f, i, a) => a.indexOf(f) === i); 

//["43000 Le Puy-en-Velay", "43000 Espaly-Saint-Marcel"]

You can find the documentation on Array.prototype.map() here.

edited Jul 23, 2019 at 8:36

answered Jul 23, 2019 at 8:06

nbokmans

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3 Comments

Yevhen Horbunkov Over a year ago

Well, I guess, upvoters and the author himself missed OP's remark 'Cities in the result should be unique'

maxd Over a year ago

The problem with just this solution is if there are multiples cities with same name it won't be filtered and it will have duplicate in the array. Cities should be unique but not postcode (this is why i used _.uniq function and then verify if it is undefined)

nbokmans Over a year ago

@maxd updated answer with filtering unique items. I don't understand what you mean by cities should be unique but not postcode, does this mean its fine if you have ["Town A - 12345", "Town A - 12344"] or not? Right now it just filters so that the combination of town and postcode is unique.

Yevhen Horbunkov · Accepted Answer · 2020-03-27 16:55:02Z

One may use

Array.prototype.map() to extract necessary properties (citycode, city) into the string
Set to get rid of duplicates

const src = {"type":"FeatureCollection","limit":20,"version":"draft","licence":"ODbL 1.0","attribution":"BAN","features":[{"type":"Feature","properties":{"importance":0.6466,"type":"municipality","adm_weight":4,"postcode":"43000","context":"43, Haute-Loire, Auvergne-Rhône-Alpes (Auvergne)","id":"43157","population":18.8,"x":769600,"y":6438600,"name":"Le Puy-en-Velay","citycode":"43157","label":"Le Puy-en-Velay","city":"Le Puy-en-Velay","score":0.8769636363636364},"geometry":{"coordinates":[3.883955,45.043141],"type":"Point"}},{"type":"Feature","properties":{"importance":0.0867,"type":"municipality","adm_weight":1,"postcode":"43000","context":"43, Haute-Loire, Auvergne-Rhône-Alpes (Auvergne)","id":"43089","population":3.6,"x":767600,"y":6438900,"name":"Espaly-Saint-Marcel","citycode":"43089","label":"Espaly-Saint-Marcel","city":"Espaly-Saint-Marcel","score":0.8260636363636362},"geometry":{"coordinates":[3.858597,45.046041],"type":"Point"}},],"query":"43000"};

const uniqueCities = obj => 
  [...new Set(obj.features.map(({properties:{city,citycode}}) => citycode+' '+city))]
 
console.log(uniqueCities(src));

.as-console-wrapper {min-height: 100%}

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