JS表达式计算一个月内所有给定数据点的平均值，对于数据点中表示的所有月份

Question

我正在寻找一个JavaScript表达式来计算一个月内所有给定数据点的平均值，即数据点中表示的所有月份的平均值。到目前为止，我只想为每个月硬编码新数组，并在其中添加12个条件，然后平均每个列表的值。但我觉得肯定有更干净更有效的方法。样本数据=（例如[YYYY，MM，DD，Value]）：

[
  [ 2020, 1, 2, 1058 ],
  [ 2020, 1, 8, 1055 ],
  [ 2020, 1, 12, 1058 ],
  [ 2020, 1, 23, 1049 ],
  [ 2020, 1, 24, 1050 ],
  [ 2020, 1, 29, 1057 ],
  [ 2020, 2, 1, 1088 ],
  [ 2020, 2, 5, 1087 ],
  [ 2020, 2, 13, 1101 ],
  [ 2020, 2, 26, 1108 ],
  [ 2020, 4, 25, 1119 ],
  [ 2020, 8, 24, 1178 ],
  [ 2020, 8, 25, 1196 ],
  [ 2020, 9, 29, 1214 ],
  [ 2020, 9, 31, 1230 ],
  [ 2020, 10, 20, 1259 ],
  [ 2020, 11, 18, 1276 ]
]

前三个字段是日期（YYYY、MM、DD）。1-12月表示为0-11，最后一个字段是将被平均的值。

我希望从表达式返回的是一个月平均值数组（例如，{month:average value}）：
[{1:avg}，{2:avg}，{4:avg}，{8:avg}，{9:avg}，{10:avg}，{11:avg}]

Answer 1

乔治的解决方案没有错，但这里有另一种方法可以通过大量的评论来实现你想要做的事情。

let source = [
  [ 2020, 1, 2, 1058 ],
  [ 2020, 1, 8, 1055 ],
  [ 2020, 1, 12, 1058 ],
  [ 2020, 1, 23, 1049 ],
  [ 2020, 1, 24, 1050 ],
  [ 2020, 1, 29, 1057 ],
  [ 2020, 2, 1, 1088 ],
  [ 2020, 2, 5, 1087 ],
  [ 2020, 2, 13, 1101 ],
  [ 2020, 2, 26, 1108 ],
  [ 2020, 4, 25, 1119 ],
  [ 2020, 8, 24, 1178 ],
  [ 2020, 8, 25, 1196 ],
  [ 2020, 9, 29, 1214 ],
  [ 2020, 9, 31, 1230 ],
  [ 2020, 10, 20, 1259 ],
  [ 2020, 11, 18, 1276 ]
];

// Object to store our output
let averages = {};

// Loop through the source data
source.forEach(row => {
  // Create an array as this month's value if not set
  if (!averages[row[1]]) 
    averages[row[1]] = [];
  
  // Lump the same-month values into the correct array. Use parseInt to avoid
  // potential NaN errors
  averages[row[1]].push(parseInt(row[3], 10));
});

// Calculate the averages by looping through each key in the object (each month),
// using reduce to get the sum of the array and then use the length property to
// get the average of that array.
Object.keys(averages).forEach(
  (m) => averages[m] = averages[m].reduce((v, i) => v + i, 0) / averages[m].length
);

// TADA!                            
console.log(averages);

Answer 2

let arr = [
  [ 2020, 1, 2, 1058 ],
  [ 2020, 1, 8, 1055 ],
  [ 2020, 1, 12, 1058 ],
  [ 2020, 1, 23, 1049 ],
  [ 2020, 1, 24, 1050 ],
  [ 2020, 1, 29, 1057 ],
  [ 2020, 2, 1, 1088 ],
  [ 2020, 2, 5, 1087 ],
  [ 2020, 2, 13, 1101 ],
  [ 2020, 2, 26, 1108 ],
  [ 2020, 4, 25, 1119 ],
  [ 2020, 8, 24, 1178 ],
  [ 2020, 8, 25, 1196 ],
  [ 2020, 9, 29, 1214 ],
  [ 2020, 9, 31, 1230 ],
  [ 2020, 10, 20, 1259 ],
  [ 2020, 11, 18, 1276 ]
];
let result = [];
let result2 = arr.reduce((res, [year, month, day, value]) => {
  if (!res[month]) {
    res[month] = { month: month, avg: 0, count: 0, sum: 0 };
    result.push(res[month])//remove this if you are satisfied with the result in result2;
  }
  res[month].sum += value;
  res[month].count +=1;
  res[month].avg = res[month].sum/res[month].count;
  return res;
} , {});
console.log('array of objects {[month, sum, count, avg]}', result);
console.log('object with values {month: {month, sum, count, avg}}', result2);