从 JSON 对象数组中异步查找 Avarage

Question

我有以下 JSON，我想找到按 deviceId 分组的平均压力：

[
    {
        "deviceId": 121,
        "Pressure": 120
    },
    {
        "deviceId": 121,
        "Pressure": 80
    },
    {
        "deviceId": 130,
        "Pressure": 20
    },
    {
        "deviceId": 130,
        "Pressure": 25
    },
    {
        "deviceId": 130,
        "Pressure": 75
    }
]

我想得到

[
    {
        "deviceId" : 121,
        "avg-Pressure": 100
    },
    {
        "deviceId": 130,
        "avg-Pressure": 40
    }
]

我怎样才能通过使用本机方法来做到这一点，我可以异步地做到这一点吗？

Answer 1

您可以将数组简化为一个对象，其中键是 deviceId，值是具有 deviceId 和压力值数组的对象：

data.reduce(
  (result,{deviceId,Pressure})=>{
    result[deviceId] = result[deviceId] || {deviceId,Pressure:[]};
    result[deviceId].Pressure.push(Pressure);
    return result;    
  },
  {}
)

然后使用Object.values 再次将其转换为数组。

然后将该数组映射到一个对象数组，其中Pressure 是一个值，因此将每个对象的压力值减少为所有压力的总和除以压力数组的长度

valuesWithArrayOfPressure.map(
  ({deviceId,Pressure})=>({
    deviceId,
    Pressure:Pressure.reduce((all,item)=>all+item,0)
  })
)

完整代码：

var data = [
    {
        "deviceId": 121,
        "Pressure": 120
    },
    {
        "deviceId": 121,
        "Pressure": 80
    },
    {
        "deviceId": 130,
        "Pressure": 20
    },
    {
        "deviceId": 130,
        "Pressure": 25
    },
    {
        "deviceId": 130,
        "Pressure": 75
    }
];

const valuesWithArrayOfPressure = data.reduce(
  (result, { deviceId, Pressure }) => {
    result[deviceId] = result[deviceId] || {
      deviceId,
      Pressure: [],
    };
    result[deviceId].Pressure.push(Pressure);
    return result;
  },
  {},
);
console.log(
  'object where Pressure is grouped',
  valuesWithArrayOfPressure,
);

console.log(
  'use values and map to get average Pressure values',
  Object.values(valuesWithArrayOfPressure).map(
    ({ deviceId, Pressure }) => ({
      deviceId,
      Pressure: Pressure.reduce(
        (all, item) => all + item,
        0,
      ),
    }),
  ),
);

Answer 2

您可以使用array#reduce 将您的数据与deviceId 以及count 和totalPressure 一起分组。然后使用array#map 计算每个deviceId 的平均压力。

const data = [ { "deviceId": 121, "Pressure": 120 }, { "deviceId": 121, "Pressure": 80 }, { "deviceId": 130, "Pressure": 20 }, { "deviceId": 130, "Pressure": 25 }, { "deviceId": 130, "Pressure": 75 } ],
      result = Object.values(data.reduce((r, {deviceId, Pressure}) => {
        r[deviceId] = r[deviceId] || {deviceId, totalPressure : 0, count : 0};
        r[deviceId].totalPressure += Pressure;
        r[deviceId].count += 1;
        return r;
      }, {}))
      .map(({deviceId, totalPressure, count}) => ({deviceId, 'avg-Pressure' : totalPressure/count}));
      
console.log(result);

Answer 3

我将 JSON 值存储在 arr 对象中。

还声明了newArray来存储结果；

我使用arr 和newArray 调用findAvaragePressure 以获取所需的结果。

// store the result here
let newArray = [];
const arr = [
    {
        "deviceId": 121,
        "Pressure": 120
    },
    {
        "deviceId": 121,
        "Pressure": 80
    },
    {
        "deviceId": 130,
        "Pressure": 20
    },
    {
        "deviceId": 130,
        "Pressure": 25
    },
    {
        "deviceId": 130,
        "Pressure": 75
    }
];

// check if the object is already token in the new array
const isAvailable = (deviceId, arr) => {
    for (let index=0; index<arr.length; index++) {
        if (arr[index].deviceId == deviceId) {
            return true;
        }
    }
    return false;
}

// for a device id, find the average pressure
const getAvarageValue = (deviceId, arr) => {
    let sum = 0;
    let count = 0;
    for (let index=0; index<arr.length; index++) {
        if (arr[index].deviceId == deviceId) {
            sum += arr[index].Pressure;
            count ++;
        }
    }
    return sum/count;
};

// put the existing array object and new resultent array
const findAvaragePressure = (arr, newArray) => {
    for (let index=0; index<arr.length; index++) {
        if (!isAvailable(arr[index].deviceId, newArray)) {
            const avg_Pressure = getAvarageValue(arr[index].deviceId, arr);
            newArray.push({
                deviceId: arr[index].deviceId,
                avg_Pressure: avg_Pressure
            });
        }
    };
    return newArray
};

const result = findAvaragePressure(arr, newArray);
console.log(result);

Answer 4

与其他答案类似，您可以尝试按deviceId 分组，并计算这些组的平均值：

const json = [{
  "deviceId": 121,
  "Pressure": 120
}, {
  "deviceId": 121,
  "Pressure": 80
}, {
  "deviceId": 130,
  "Pressure": 20
}, {
  "deviceId": 130,
  "Pressure": 25
}, {
  "deviceId": 130,
  "Pressure": 75
}]

const deviceGroups = {};
for (const key in json) {
  deviceId = json[key].deviceId;

  if (!deviceGroups[deviceId]) {
    deviceGroups[deviceId] = []
  }

  deviceGroups[deviceId].push(json[key])
}

result = [];
for (const [key, value] of Object.entries(deviceGroups)) {
  const jsonObject = {
    "deviceId": key
  };

  let sum = 0;
  for (const array in deviceGroups[key]) {
    sum += deviceGroups[key][array].Pressure;
  }

  jsonObject["avg-Pressure"] = sum / deviceGroups[key].length;
  result.push(jsonObject);
}

console.log(result);