MongoDB Aggregation leap-year - mongodb

Question

I am learning MongoDB NoSQL, and I have a problema about it.
Consider these documents:
{
"_id" : ObjectId("63a994974ac549c5ea982d2b"),
"title" : "Destroyer",
"year" : 2018
},
{
"_id" : ObjectId("63a994974ac549c5ea982d2a"),
"title" : "Aquaman",
"year" : 2014
},
{
"_id" : ObjectId("63a994974ac549c5ea982d29"),
"title" : "On the Basis of Sex",
"year" : 1996
},
{
"_id" : ObjectId("63a994974ac549c5ea982d28"),
"title" : "Holmes and Watson",
"year" : 1940
},
{
"_id" : ObjectId("63a994974ac549c5ea982d27"),
"title" : "Conundrum: Secrets Among Friends",
"year" : 1957
},
{
"_id" : ObjectId("63a994974ac549c5ea982d26"),
"title" : "Welcome to Marwen",
"year" : 2000
},
{
"_id" : ObjectId("63a994974ac549c5ea982d25"),
"title" : "Mary Poppins Returns",
"year" : 1997
},
{
"_id" : ObjectId("63a994974ac549c5ea982d24"),
"title" : "Bumblebee",
"year" : 2004
},
I am trying to get all title that they have a leap year and I want to get the "count" of all title.
So, I tried this code:
var q1 = {$project: {
leap: {
"$and": [
"$eq": ["$divide"["$year", 4], 0],
{
"$or":[{"$ne": ["$divide"["$year",100],0]},
{"$eq": ["$divide"["$year", 400],0]}]
}
]
}
}}
var q2 = {$group: {"_id": null, "total": {$sum:1}}}
var etapas = [q1,q2]
db.genres.aggregate(etapas)
But, with this code, I only get in 'q1', the variable 'leap', all false conditionals. So, I do not know how to get the year when the logical operator is true or false. Even more, I want to count all the leap years of the documents I have been given before.
The expect output for the documents before is this:
{
"_id": leap year
"count": 3
}
How can I do that? How can I type when I've got a false result?
Thanks so much for your attention in this problem. Whatever ask you need, do it without any problem.

Answer 1

To check if a number is divisible by another, you need to see if the remainder is 0 using $mod, such as:
db.collection.aggregate([
{$project: {
leap: {
"$and": [
{"$eq": [{"$mod": ["$year",4]}, 0]},
{"$or": [
{"$ne": [{"$mod": ["$year", 100]}, 0]},
{"$eq": [{"$mod": ["$year", 400]}, 0] }
]}
]
}
}},
{$group: {
"_id": "$leap",
"total": {$sum: 1}
}}
])
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