如何计算对象的匹配唯一键数（javascript）

Question

I'm trying to get the unique keys of an object, add the values and count how many of the unique key there are of each, but can't figure out a graceful solution.

raw array of objs:

[{
    "2017W40": 15.25
}, {
    "2017W40": 16.5
}, {
    "2017W40": 16.6
}, {
    "2017W40": 11
}, {
    "2017W40": 17.857142857142858
}, {
    "2017W40": 13
}, {
    "2017W41": 19
}, {
    "2017W41": 20.25
}, {
    "2017W41": 18.25
}, {
    "2017W41": 13
}, {
    "2017W41": 20.333333333333332
}, {
    "2017W41": 20.5
}, {
    "2017W41": 20.5
}, {
    "2017W42": 19.5
}, {
    "2017W42": 19.5
}, {
    "2017W42": 20
}, {
    "2017W42": 19.5
}, {
    "2017W42": 19.333333333333332
}, {
    "2017W42": 20
}, {
    "2017W42": 20.5
}, {
    "2017W43": 20
}, {
    "2017W43": 20
}, {
    "2017W43": 19.666666666666668
}, {
    "2017W43": 19.6
}, {
    "2017W43": 19.666666666666668
}, {
    "2017W43": 19
}, {
    "2017W43": 19.5
}, {
    "2017W44": 21
}, {
    "2017W44": 19.5
}, {
    "2017W44": 20
}, {
    "2017W44": 19.5
}]

summed object:

{
    "2017W40": 90.20714285714286,
    "2017W41": 131.83333333333331,
    "2017W42": 138.33333333333331,
    "2017W43": 137.43333333333334,
    "2017W44": 80
}

But I'd also like to include a count of each (so I can get an average instead of just the sum) Here is the method I"m using:

function getValueAvg(valsByKey) {
  const dateObj = {};
  for (let i = 0; i < valsByKey.length; ++i) {
    for (const obj in valsByKey[i]) {
      if (dateObj[obj]) {
        // add them if exists already
        dateObj[obj] = dateObj[obj] + valsByKey[i][obj];
      } else {
        // first
        dateObj[obj] = valsByKey[i][obj];
      }
    }
  }

So either a final object of

{
    {"2017W40": 90.20714285714286, count:x},
    {"2017W41": 131.83333333333331, count:x},
    {"2017W42": 138.33333333333331, count:x},
    {"2017W43": 137.43333333333334, count:x},
    {"2017W44": 80, count:x}
}

or just the value divided by count would work wonders for me. "2017W40": 90.20714285714286/count

Answer 1

You can just create new objects that has two fields, a value or sum field, and a count field. When you iterate over the data, you just add into the value field and then up the count by one.

 function getValueAvg(valsByKey) { const dateObj = {}; for (let i = 0; i < valsByKey.length; ++i) { for (const obj in valsByKey[i]) { if (dateObj[obj]) { // add them if exists already dateObj[obj].val = dateObj[obj].val + valsByKey[i][obj]; dateObj[obj].count += 1; } else { // first dateObj[obj] = {"val":valsByKey[i][obj], "count":1}; } } } return dateObj; } var data = [{ "2017W40": 15.25 }, { "2017W40": 16.5 }, { "2017W40": 16.6 }, { "2017W40": 11 }, { "2017W40": 17.857142857142858 }, { "2017W40": 13 }, { "2017W41": 19 }, { "2017W41": 20.25 }, { "2017W41": 18.25 }, { "2017W41": 13 }, { "2017W41": 20.333333333333332 }, { "2017W41": 20.5 }, { "2017W41": 20.5 }, { "2017W42": 19.5 }, { "2017W42": 19.5 }, { "2017W42": 20 }, { "2017W42": 19.5 }, { "2017W42": 19.333333333333332 }, { "2017W42": 20 }, { "2017W42": 20.5 }, { "2017W43": 20 }, { "2017W43": 20 }, { "2017W43": 19.666666666666668 }, { "2017W43": 19.6 }, { "2017W43": 19.666666666666668 }, { "2017W43": 19 }, { "2017W43": 19.5 }, { "2017W44": 21 }, { "2017W44": 19.5 }, { "2017W44": 20 }, { "2017W44": 19.5 }] console.log(getValueAvg(data));