Remove the second occurance of an object from an object array

I have an array of what I call fareZone objects. Each fare zone object has an array of stops.

I wish to keep the first occurrence of a stop object and remove all other occurrences of the same object (same meaning it has the same atcoCode) from the array.

Object Array

const fareZones = [{
    name: 'Zone 1',
    stops: [{
            stopName: 'Ashton Bus Station',
            atcoCode: '1800EHQ0081',
        },
        {
            stopName: 'New Street',
            atcoCode: '1800EHQ0721',
        },
        {
            stopName: 'Farfield Road',
            atcoCode: '1800EHQ0722',
        },
        {
            stopName: 'Ashton Bus Station',
            atcoCode: '1800EHQ0081',
        },
        {
            stopName: 'New Street',
            atcoCode: '1800EHQ0041',
        },
    ],
    prices: [],
},
{
    name: 'Zone 2',
    stops: [{
        stopName: 'Henrietta Street',
        atcoCode: '1800EH24201',
     
    }, ],
    prices: [],
},
{
    name: 'Zone 3',
    stops: [{
            stopName: 'Crickets Ln',
            atcoCode: '1800EH24151',
        },
        {
            stopName: 'Tameside College',
            atcoCode: '1800EH21241',            
        },
        {
            stopName: 'Ashton Bus Station',
            atcoCode: '1800EHQ0081',            
        },
    ],
    prices: [],
}]

Desired outcome

const fareZones = [{
    name: 'Zone 1',
    stops: [{
            stopName: 'Ashton Bus Station',
            atcoCode: '1800EHQ0081',
        },
        {
            stopName: 'New Street',
            atcoCode: '1800EHQ0721',
        },
        {
            stopName: 'Farfield Road',
            atcoCode: '1800EHQ0722',
        },
        {
            stopName: 'New Street',
            atcoCode: '1800EHQ0041',
        },
    ],
    prices: [],
},
{
    name: 'Zone 2',
    stops: [{
        stopName: 'Henrietta Street',
        atcoCode: '1800EH24201',
     
    }, ],
    prices: [],
},
{
    name: 'Zone 3',
    stops: [{
            stopName: 'Crickets Ln',
            atcoCode: '1800EH24151',
        },
        {
            stopName: 'Tameside College',
            atcoCode: '1800EH21241',            
        },
        {
            stopName: 'Ashton Bus Station',
            atcoCode: '1800EHQ0081',            
        },
    ],
    prices: [],
}]

Notice how the third stop in Zone 1 was removed because it was a duplicate.

How do I achieve this in JavaScript?

Current Progress

// for each fare stage, check to see if we have duplicate stops
fareZones.map((fz) => {
    let stopsWithinFareZone = fz.stops;

    const atcoCodesOfStopsWithinFareZone = stopsWithinFareZone.map((s) => s.atcoCode);

    const hasDuplicateStops = hasDuplicates(atcoCodesOfStopsWithinFareZone);

    if (hasDuplicateStops) {
        // so we have duplicates, how do I keep the first occurrence
        // and remove all other occurrences of the duplicate stop
    }
});

export const hasDuplicates = (array: string[]): boolean => {
    return new Set(array).size !== array.length;
};

>Solution :

You can easily achieve the result using Set and filter as:

const result = fareZones.map((fareZone) => {
      const set = new Set();
      const stops = fareZone.stops.filter((o) => {
        if (!set.has(o.atcoCode)) {
          set.add(o.atcoCode);
          return true;
        } else return false;
      });
      return { ...fareZone, stops };
    });

const fareZones = [
  {
    name: "Zone 1",
    stops: [
      {
        stopName: "Ashton Bus Station",
        atcoCode: "1800EHQ0081",
      },
      {
        stopName: "New Street",
        atcoCode: "1800EHQ0721",
      },
      {
        stopName: "Farfield Road",
        atcoCode: "1800EHQ0722",
      },
      {
        stopName: "Ashton Bus Station",
        atcoCode: "1800EHQ0081",
      },
      {
        stopName: "New Street",
        atcoCode: "1800EHQ0041",
      },
    ],
    prices: [],
  },
  {
    name: "Zone 2",
    stops: [
      {
        stopName: "Henrietta Street",
        atcoCode: "1800EH24201",
      },
    ],
    prices: [],
  },
  {
    name: "Zone 3",
    stops: [
      {
        stopName: "Crickets Ln",
        atcoCode: "1800EH24151",
      },
      {
        stopName: "Tameside College",
        atcoCode: "1800EH21241",
      },
      {
        stopName: "Ashton Bus Station",
        atcoCode: "1800EHQ0081",
      },
    ],
    prices: [],
  },
];

const result = fareZones.map((fareZone) => {
  const set = new Set();
  const stops = fareZone.stops.filter((o) => {
    if (!set.has(o.atcoCode)) {
      set.add(o.atcoCode);
      return true;
    } else return false;
  });
  return { ...fareZone, stops };
});

console.log(result);