JavaScriptはJSONオブジェクトを2つのプロパティでグループ化し、カウントします

このようなオブジェクトの配列があるとします-

const arr = [
   {"location":"Kirrawee","identity_long":"student"},
   {"location":"Kirrawee","identity_long":"visitor"},
   {"location":"Kirrawee","identity_long":"visitor"},
   {"location":"Kirrawee","identity_long":"worker"},
   {"location":"Sutherland","identity_long":"student"},
   {"location":"Sutherland","identity_long":"resident"},
   {"location":"Sutherland","identity_long":"worker"},
   {"location":"Sutherland","identity_long":"resident"},
   {"location":"Miranda","identity_long":"resident"},
   {"location":"Miranda","identity_long":"worker"},
   {"location":"Miranda","identity_long":"student"},
   {"location":"Miranda","identity_long":""},
   {"location":"Miranda","identity_long":"worker"},
   {"location":"Miranda","identity_long":"resident"}
];

そのようなオブジェクトの配列を1つ取り込むJavaScript関数を作成する必要があります。関数は、すべての（同一の）オブジェクトがlocationプロパティに基づいてグループ化されたオブジェクトの新しい配列を準備する必要があります。

また、オブジェクトには、オブジェクトの元の配列に出現した回数を含むcountプロパティを割り当てる必要があります。

したがって、上記の配列の場合、出力は次のようになります-

const output = [
   {"location":"Kirrawee","identity":"student","count":1},
   {"location":"Kirrawee","identity":"visitor","count":2},
   {"location":"Kirrawee","identity":"worker","count":1},
   {"location":"Sutherland","identity":"student","count":1},
   {"location":"Sutherland","identity":"resident","count":2},
   {"location":"Sutherland","identity":"worker","count":1},
   {"location":"Miranda","identity":"resident","count":2},
   {"location":"Miranda","identity":"worker","count":2},
   {"location":"Miranda","identity":"student","count":1}
];

例

このためのコードは-

const arr = [
   {"location":"Kirrawee","identity_long":"student"},
   {"location":"Kirrawee","identity_long":"visitor"},
   {"location":"Kirrawee","identity_long":"visitor"},
   {"location":"Kirrawee","identity_long":"worker"},
   {"location":"Sutherland","identity_long":"student"},
   {"location":"Sutherland","identity_long":"resident"},
   {"location":"Sutherland","identity_long":"worker"},
   {"location":"Sutherland","identity_long":"resident"},
   {"location":"Miranda","identity_long":"resident"},
   {"location":"Miranda","identity_long":"worker"},
   {"location":"Miranda","identity_long":"student"},
   {"location":"Miranda","identity_long":""},
   {"location":"Miranda","identity_long":"worker"},
   {"location":"Miranda","identity_long":"resident"}
];
const groupArray = (arr = []) => {
   // create map
   let map = new Map()
   for (let i = 0; i < arr.length; i++) {
      const s = JSON.stringify(arr[i]);
      if (!map.has(s)) {
         map.set(s, {
            location: arr[i].location,
            identity: arr[i].identity_long,
            count: 1,
         });
      } else {
         map.get(s).count++;
      }
   }
   const res = Array.from(map.values())
   return res;
};
console.log(groupArray(arr));

出力

そして、コンソールの出力は-

[
   { location: 'Kirrawee', identity: 'student', count: 1 },
   { location: 'Kirrawee', identity: 'visitor', count: 2 },
   { location: 'Kirrawee', identity: 'worker', count: 1 },
   { location: 'Sutherland', identity: 'student', count: 1 },
   { location: 'Sutherland', identity: 'resident', count: 2 },
   { location: 'Sutherland', identity: 'worker', count: 1 },
   { location: 'Miranda', identity: 'resident', count: 2 },
   { location: 'Miranda', identity: 'worker', count: 2 },
   { location: 'Miranda', identity: 'student', count: 1 },
   { location: 'Miranda', identity: '', count: 1 }
]