javascript - 如何使用 underscorejs 分组并获得平均值

Question

如何使用下划线对category进行分组并取平均值？

我有一个对象数组。它应该按 category 分组，Analytics 的平均值是根据 val 属性计算的，即 1+2 => 3. 3/total类别数。所以，3/2 => 1.5

预期输出:{ Analytics: 1.5 }

[{
  area:"Digital",
  category:"Analytics",
  qId:"wRHmpHHGzrYLsCEJ3",
  type:"Reorganize",
  userId:"M4JEJGiPZ8e9om9A",
  val:1
},
{
  area:"Digital",
  category:"Analytics",
  qId:"wRHmpHHGzrYLsCEJ3",
  type:"Reorganize",
  userId:"M4JEJGiPZ8e9om9A",
  val:2
}]

谢谢

Answer 1

您可以 group the objects by category , 然后 iterate over all the keys in this resulting object和 reduce the values :

var types = _.groupBy(array, 'category');
var result = _.mapObject(types, function(val, key) {
  return _.reduce(val, function(memo, v) { 
    return memo + v.val; 
  }, 0) / val.length;
});

var array = [{
  area:"Digital",
  category:"Analytics",
  qId:"wRHmpHHGzrYLsCEJ3",
  type:"Reorganize",
  userId:"M4JEJGiPZ8e9om9A",
  val:1
},
{
  area:"Digital",
  category:"Analytics",
  qId:"wRHmpHHGzrYLsCEJ3",
  type:"Reorganize",
  userId:"M4JEJGiPZ8e9om9A",
  val:2
}];

var types = _.groupBy(array, 'category');
var result = _.mapObject(types, function(val, key) {
  return _.reduce(val, function(memo, v) { 
    return memo + v.val; 
  }, 0) / val.length;
});

console.log(result);

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