reduce_objects.js

/** building.json
{
"results" = [    {
      "attributes": {
        "BUILDING": "B041",
        .....
      }
    },
    {
      "attributes": {
        "BUILDING": "B071",
        ....
    },
    {
      "attributes": {
        "BUILDING": "B111",
        ....
      }
    },
    {
      "attributes": {
        "BUILDING": "B111"
        .....
      }
    }]
}
*/

const buildingJson = require('./building');
const buildingObject = (id) => {
  return {
    id: id,
    idNumber: id.substring(1),
  };
};

const reduceBuildings = (buildings) => {
  return buildings.reduce((groups, building) => {
    const idNumber = building.idNumber;
    const id = building.id;
    const group = groups.find(g => g.idNumber === idNumber);

    if (group) {
      return groups;
    }

    groups.push({
      id: id,
      idNumber: idNumber,
    });
    return groups;
  }, []);
};

const buildings = (buildingJson.results.map(b => buildingObject(b.attributes.BUILDING)));
const buildingNumbers = reduceBuildings(buildings);
console.log(JSON.stringify(buildingNumbers));