Javascript 按键计算对象数组的百分比总计

Question

假设我在 Javascript 中有以下数据结构:

 const data = [
       {year: 2017, kind: "mammal", animal: "dog", total: 5},
       {year: 2017, kind: "mammal", animal: "dog", total: 3},
       {year: 2016, kind: "mammal", animal: "dog", total: 5},
       {year: 2016, kind: "bird", animal: "chicken", total: 5},
       {year: 2016, kind: "bird", animal: "chicken", total: 90}
 ];

我希望能够指定一个或多个键(例如year)来对数据进行分组。因此，如果我只是将 year 指定为分组依据，我希望计算总数如下:

 [{year: 2017, kind: "mammal", animal: "dog", count: 8, pct: 1},
  {year: 2016, kind: "mammal", animal: "dog", count: 5, pct: 0.05},
  {year: 2016, kind: "bird", animal: "chicken", count: 95, pct: 0.95}]

或者，如果我按年份和种类指定组总数，我需要以下内容:

 [{year: 2017, kind: "mammal", animal: "dog", count: 8, pct: 1},
  {year: 2016, kind: "mammal", animal: "dog", count: 5, pct: 1},
  {year: 2016, kind: "bird", animal: "chicken", count: 95, pct: 1}]

我如何在 Javascript 中实现这个？我已经考虑过使用 d3 的嵌套函数，但到目前为止还没有成功地理解实现。

Answer 1

我认为在尝试实现它之前，你需要清楚地弄清楚你的需求。根据您的描述，我的理解是，对于结果，年份+种类+动物是结果项的关键。并且您指定的组仅用于计算百分比。

首先根据年份+种类+动物对项目进行分组

function groupItems(data){
   var resultMap = {};
   for(var index in data){
      var item = data[index];
      var key = item['year']+'###'+item['kind']+'###'+item['animal'];
      if(!resultMap[key]){
         //copy the item to a new object to make sure it does not update the origin data
         resultMap[key] = Object.assign({}, item); 
      }else{
         // sum them up
         resultMap[key]['total'] = resultMap[key]['total'] +item['total'];
      }
   }
   return Object.values(resultMap);
}

现在我们有了项目，您需要的是根据指定的组计算百分比。

function computePercentage(groupedItems, withGroups){
    //compute the total items per specified group
    var totalItemsPerGroup = {};
    for(var index in groupedItems){
        var item = groupedItems[index];
        var keyValues = getValuesFromObjectWithKeys(item, withGroups);
        var strKey = keyValues.join('###');
        if(totalItemsPerGroup[strKey] != undefined){
            totalItemsPerGroup[strKey] += item['total'];
        }else{
            totalItemsPerGroup[strKey] = item['total'];
        }
    }
    // compute percentage based on the total items per specified group calculated
    var result = [];
    for(var index in groupedItems){
        var item = groupedItems[index];
        var keyValues = getValuesFromObjectWithKeys(item, withGroups);
        var strKey = keyValues.join('###');
        var totalCount = totalItemsPerGroup[strKey];
        var percentage = totalCount == 0 ? 0 : item['total'] / totalCount;
        var resultItem = {};
        resultItem['year'] = item['year'];
        resultItem['kind'] = item['kind'];
        resultItem['animal'] = item['animal'];
        resultItem['count'] = item['total'];
        resultItem['pct'] = percentage;
        result.push(resultItem);
    }  
    return result;
}

// a helper function to get values based on specified keys
function getValuesFromObjectWithKeys(obj, keys){
   var result = [];
   for(var i in keys){
       if(obj[keys[i]]){
           result.push(obj[keys[i]]);
       }
   }
   return result;
}

因此要使用这些功能:

var grouppedItems = groupItems(data);
var yearPercentage = computePercentage(grouppedItems , ['year']);
console.log(JSON.stringify(yearPercentage));
var yearKindPercentage = computePercentage(grouppedItems , ['year', 'kind']);
console.log(JSON.stringify(yearKindPercentage ));
var kindAnimalPercentage = computePercentage(grouppedItems , ['kind', 'animal']);
console.log(JSON.stringify(kindAnimalPercentage ));