如何使用節點-js使用聚合函數

Question

我有一個json，其數組被稱爲chargeamountunitLevel。我想由chargeAmountUnit.The輸入JSON分組總結行動的chargeAmount：

"chargeamountunitLevel": [ 
     { 
      "chargeAmount": 4, 
      "chargeAmountUnit": "per hour", 
      "currencyCode": "USD" 
     }, 
     { 
      "chargeAmount": 50, 
      "chargeAmountUnit": "per hour", 
      "currencyCode": "USD" 
     }, 
     { 
      "chargeAmount": 25, 
      "chargeAmountUnit": "per month", 
      "currencyCode": "USD" 
     }, 
     { 
      "chargeAmount": 25, 
      "chargeAmountUnit": "per month", 
      "currencyCode": "USD" 
     } 

    ] 

結果可能如下：

"chargeamountunitLevel": [ 
     { 
      "chargeAmount": 54, 
      "chargeAmountUnit": "per hour", 
      "currencyCode": "USD" 
     }, 
     { 
      "chargeAmount": 50, 
      "chargeAmountUnit": "per month", 
      "currencyCode": "USD" 
     } 

     ] 

有什麼建議？

Answer 1

你總是可以利用reduce功能。因爲我們提供了initialValue作爲reduce的第二個參數，所以第一次調用callback時，該值將作爲result參數傳遞。然後對於所有後續呼叫，result將成爲先前呼叫的返回值。

這裏我們基本上檢查我們的initialValue對象，如果chargeAmountUnit的o已經存在作爲一個關鍵。如果沒有，我們創建一個具有相同屬性值的對象o的新對象，並使用chargeAmountUnit作爲關鍵字將其放入我們的initialValue對象中。但是，如果它確實存在，我們使用chargeAmountUnit作爲關鍵字檢索先前創建的對象，並簡單地總結相關的值。

此外，您可能已經注意到，我們正在推動在一個陣列中創建的對象，這是因爲在最後，你想數組作爲一個結果，而不是像這樣：

{ 
    'per month': {...}, 
    'per hour': {...} 
} 

這裏是如何做到這一點：

data.reduce(function (result, o) { 
    var unit = o.chargeAmountUnit; 
    if (!(unit in result)) { 
     result.arr.push(result[unit] = { 
      chargeAmountUnit: unit, 
      chargeAmount: o.chargeAmount, 
      currencyCode: o.currencyCode 
     }); 
    } else { 
     result[unit].chargeAmount += o.chargeAmount; 
    } 

    return result; 
}, { arr: [] }).arr; 

編輯：由多個字段組，你可以簡單地通過key由場字符串值concanating組創建一個組。

以下將分組在chargeAmountUnit和currencyCode。

data.reduce(function (result, o) { 
    //compute group by key 
    var key = o.chargeAmountUnit + o.currencyCode; 
    if (!(key in result)) { 
     result.arr.push(result[key] = { 
      chargeAmountUnit: o.chargeAmountUnit, 
      chargeAmount: o.chargeAmount, 
      currencyCode: o.currencyCode 
     }); 
    } else { 
     result[key].chargeAmount += o.chargeAmount; 
    } 

    return result; 
}, { arr: [] }).arr; 

Answer 2

可以使用underscore.js

這裏是代碼：

var _ = require('underscore'); // use `npm install underscore` 
var util = require('util');  // nodejs default modules 

var data = { 
    "chargeamountunitLevel": [{ 
    "chargeAmount": 4, 
    "chargeAmountUnit": "per hour", 
    "currencyCode": "USD" 
    } 
    , { 
    "chargeAmount": 50, 
    "chargeAmountUnit": "per hour", 
    "currencyCode": "USD" 
    } 
    , { 
    "chargeAmount": 25, 
    "chargeAmountUnit": "per month", 
    "currencyCode": "USD" 
    } 
    , { 
    "chargeAmount": 10, 
    "chargeAmountUnit": "per month", 
    "currencyCode": "USD" 
    } 
    , { 
    "chargeAmount": 1, 
    "chargeAmountUnit": "per month", 
    "currencyCode": "RMB" 
    } 
    , { 
    "chargeAmount": 25, 
    "chargeAmountUnit": "per month", 
    "currencyCode": "HKD" 
    }] 
}; 

// This should give you an array of objects that 
// are grouped by chargeAmountUnit. 
var tmp = _.groupBy(data["chargeamountunitLevel"], function(d){ 
    return d["chargeAmountUnit"]; 
}); 
// Show the temporary result :o) 
console.log(tmp); 

// Now group the result with currency code 
var tmp2 = {}; 
_.each(tmp, function(t, unit){ 
    tmp2[unit] = _.groupBy(t, function(d){ 
    return d["currencyCode"]; 
    }); 
}); 

// show the temp result again 
console.log("tmp2: \n" + util.inspect(tmp2, false, null, true)); // util.inspect() is different in node v0.10.x 

var finalResult = []; 
_.each(tmp2, function(t, unit){ 
    _.each(t, function(items, currency){ 
    var total = 0; 
    _.each(items, function(item){ 
     total += item["chargeAmount"];  // should also * currencyCode? 
    }); 
    finalResult.push({ 
     "chargeAmountUnit" : unit 
     , "chargeAmount" : total 
     , "currencyCode" : currency // Update it yourself :o) 
    }); 
    }); 
}); 

console.log(finalResult);