JavaScript按两个属性对JSON对象进行分组并计数

我有一个如下所示的JSON对象：

long_array =    
[
{"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"}
];

我要实现的对象如下：

grouped_and_counted_location_and_identity =
[
{"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}
];

我发现这在R语言中非常容易实现，我会这样做：

long_array %>%
    group_by(location, identity_long) %>%
    summarise(n = n())

甚至只是

long_array %>%
    count(location, identity_long)

但是我如何在Java脚本中实现这一点？

我只想按两个属性对JSON对象进行分组，并计算相同出现的次数。

---

解决方案

您可以使用库(如loDash)并使用其GROUP BY函数来实现此简单方法，但实现您自己的GROUP BY函数会比较耗时。

数据-lang="js"数据-隐藏="假"数据-控制台="真"数据-巴贝尔="假">

let long_array = [{
    "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"
  }
];

function addItemCounts(items, groupByKeys) {
  var groups = _.groupBy(long_array, obj => {
    return groupByKeys.map(key => obj[key]).join('-');
  });

  return _.map(groups, g => ({
    ...g[0],
    count: g.length
  }));
}

console.log(addItemCounts(long_array, ['identity_long', 'location']));

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