如何计算每个国家使用猫鼬的重复次数？

Question

My following code is able to count the number of distinct cities.

Get distinct countries

    IpDetails.find().distinct('city', function(error, cities) {
    console.log(`unique cities is:, ${cities}`)
})

Results

unique cities is: Toronto, Waterloo

My question is, how do I get the number of times that Toronto and Waterloo appeared in my database using mongoose? Could anyone advise?

Answer 1

You should be able to do this using $aggregate with $group and $sum . Effectively you would group each object by the the value of city and increment the count for each:

IpDetails.aggregate([
  { $group: { _id: "$city", count: { $sum: 1 } } }],
  function(error, groups) {
    groups.forEach(function(group) {
      console.log(`City ${group._id} appeared ${group.count} times`);
    });
  }
);

Hopefully that helps!