$round is rounding down to even numbers even when it's above the .5 threshold

[praoshealth]

 const pipeline = [
  {
    $project: {
      "10_4": { $round: [10.4, 0] },
      "10_5": { $round: [10.5, 0] },
      "10_6": { $round: [10.6, 0] },
      "10_7": { $round: [10.7, 0] },
      "11_4": { $round: [11.4, 0] },
      "11_5": { $round: [11.5, 0] },
      "11_6": { $round: [11.9, 0] },
  }
} ];

const result = new mingo.Aggregator(pipeline).run([{}]);

console.log(result);

Actual Results

[
  {
    '10_4': 10,
    '10_5': 10,
    '10_6': 10,
    '10_7': 10,
    '11_4': 11,
    '11_5': 12,
    '11_6': 12
  }
]

Expected Results

[
  {
    '10_4': 10,
    '10_5': 10,
    '10_6': 11,
    '10_7': 11,
    '11_4': 11,
    '11_5': 12,
    '11_6': 12
  }
]

Also MongoDb seems to have an undocumented feature where if you pass in a numerical value instead of an array it defaults to a precision of 0

 const pipeline = [
  {
    $project: {
      "10_4": { $round: 10.4 }
  }
} ];

const result = new mingo.Aggregator(pipeline).run([{}]);

console.log(result);

Actual Results

[{}]

Expected Results

[
  {
    '10_4': 10
  }
]

[kofrasa]

Thanks for the report @praoshealth.

Unfortunately, this is one of those problems that is hard to fix comprehensibly given how floating point arithmetic works in JS. See #305 and the question posed on the MongoDB forum.

I think we can find an implementation that will be accurate for the given values, but I suspect there will still be a range of values that will round incorrectly with different decimal places. That said, I am happy to switch to an implementation which we think is better if the error rate is lowest for 4 or fewer decimal places which is reasonable in my view.

The relevant code is here if you wanna take a stab at it.

[praoshealth]

#348

[kofrasa]

Thanks for the PR. Happy to merge it with some expanded test coverage. Please include your examples.

    // https://github.com/kofrasa/mingo/issues/347
    [[10.4, 0], 10],
    [[10.5, 0], 10],
    [[10.6, 0], 11],
    [[10.7, 0], 11],
    [[11.4, 0], 11],
    [[11.5, 0], 12],
    [[11.9, 0], 12]

[kofrasa]

Resolved in 6.4.3. Thanks for the contribution.