I have below collection structure and I want to find minimum score for each student.
>db.students.findOne()
{
"_id" : 0,
"name" : "aimee Zank",
"scores" : [
{
"type" : "exam",
"score" : 1.463179736705023
},
{
"type" : "quiz",
"score" : 11.78273309957772
},
{
"type" : "homework",
"score" : 6.676176060654615
},
{
"type" : "homework",
"score" : 35.8740349954354
}
]
}
I use below aggregate command
db.students.aggregate([
{
$group: {_id: "$_id" , min: {$min: '$scores.score'}}
}
])
below is the output:
{ "_id" : 199, "min" : [ 82.11742562118049, 49.61295450928224, 28.86823689842918, 5.861613903793295 ] }
{ "_id" : 198, "min" : [ 11.9075674046519, 20.51879961777022, 55.85952928204192, 64.85650354990375 ] }
{ "_id" : 95, "min" : [ 8.58858127638702, 88.40377630359677, 25.71387474240768, 23.73786528217532 ] }
{ "_id" : 11, "min" : [ 78.42617835651868, 82.58372817930675, 87.49924733328717, 15.81264595052612 ] }
{ "_id" : 94, "min" : [ 6.867644836612586, 63.4908039680606, 85.41865347441522, 26.82623527074511 ] }
it returns all scores for each student instead of the minimum one. What wrong with my query command? I am using mongo 3.4.
After some searching, I found that the solution is to add $unwind on scores.score. The complete command is:
stus = db.students.aggregate([
{
"$unwind": "$scores"
},
{
$group: {_id: "$_id" , minScore: {$min: '$scores.score'}}
}
])
Related
This is an example of the collection I am working with
> db.grades.find().limit(5).forEach(printjson)
{
"_id" : ObjectId("50b59cd75bed76f46522c353"),
"student_id" : 0,
"class_id" : 30,
"scores" : [
{
"type" : "exam",
"score" : 14.34345947841966
},
{
"type" : "quiz",
"score" : 47.65945482174327
},
{
"type" : "homework",
"score" : 83.42772189120254
},
{
"type" : "homework",
"score" : 49.86812935368258
},
{
"type" : "homework",
"score" : 39.85525554437086
}
]
}
{
"_id" : ObjectId("50b59cd75bed76f46522c356"),
"student_id" : 0,
"class_id" : 27,
"scores" : [
{
"type" : "exam",
"score" : 60.19473636151568
},
{
"type" : "quiz",
"score" : 64.15966210014162
},
{
"type" : "homework",
"score" : 82.80835343023551
}
]
}
{
"_id" : ObjectId("50b59cd75bed76f46522c350"),
"student_id" : 0,
"class_id" : 5,
"scores" : [
{
"type" : "exam",
"score" : 88.22950674232497
},
{
"type" : "quiz",
"score" : 79.28962650427184
},
{
"type" : "homework",
"score" : 18.66254946562674
},
{
"type" : "homework",
"score" : 40.28154176513361
},
{
"type" : "homework",
"score" : 1.23735944117882
},
{
"type" : "homework",
"score" : 88.96101200683958
}
]
}
{
"_id" : ObjectId("50b59cd75bed76f46522c357"),
"student_id" : 0,
"class_id" : 11,
"scores" : [
{
"type" : "exam",
"score" : 58.83297411100884
},
{
"type" : "quiz",
"score" : 49.66835710930263
},
{
"type" : "homework",
"score" : 18.05861540807023
},
{
"type" : "homework",
"score" : 80.04086698967356
}
]
}
{
"_id" : ObjectId("50b59cd75bed76f46522c358"),
"student_id" : 0,
"class_id" : 10,
"scores" : [
{
"type" : "exam",
"score" : 30.93065784731665
},
{
"type" : "quiz",
"score" : 55.98003281528393
},
{
"type" : "homework",
"score" : 55.6752702814148
},
{
"type" : "homework",
"score" : 63.15391302252755
}
]
}
What I'm trying to achieve, is to get the highest score of the exam, where the student id is 5. I've been stuck on this for quite a while, and the furthest I've managed to come is to retrieve all of the student's exam scores, however I haven't managed to make it so only the highest scoring one displays. This is another aspect I'm stuck on.
This is the code for this output:
{
"student_id" : 5,
"class_id" : 18,
"scores" : [
{
"type" : "exam",
"score" : 73.04238861317688
}
]
}
{
"student_id" : 5,
"class_id" : 8,
"scores" : [
{
"type" : "exam",
"score" : 22.38732080941065
}
]
}
{
"student_id" : 5,
"class_id" : 0,
"scores" : [
{
"type" : "exam",
"score" : 43.64758440439862
}
]
}
{
"student_id" : 5,
"class_id" : 16,
"scores" : [
{
"type" : "exam",
"score" : 33.39752665396672
}
]
}
{
"student_id" : 5,
"class_id" : 30,
"scores" : [
{
"type" : "exam",
"score" : 73.48459944869943
}
]
}
{
"student_id" : 5,
"class_id" : 19,
"scores" : [
{
"type" : "exam",
"score" : 15.36563152024366
}
]
}
{
"student_id" : 5,
"class_id" : 23,
"scores" : [
{
"type" : "exam",
"score" : 21.58296008740177
}
]
}
The code that gets me this is as follows:
var pipeline = [
{ $match: {student_id: 5} },
{ $unwind: "$scores" },
{ $group: {
_id: "$_id",
"student_id": { "$first": "$student_id" },
"class_id": { "$first": "$class_id" },
scores: { $push: "$scores" } } },
{ $project: { _id: 0,
student_id: 1,
class_id: 1,
scores: { $slice: [ "$scores", 1] } } } ];
var results = db.grades.aggregate ( pipeline );
results.forEach(printjson)
(Sorry for the poor structuring, I did my best but I'm not used too it on stackoverflow)
I've been coding with MongoDB for about 2 days now, and I'm knowledgeable in it. Even less so with aggregates, but looking at posts and other code this seemed like the way to do it. From my point of view, because I'm already slicing through it, and attempting to sort the score will only result in getting the highest score out of exams, quiz and homeworks, so it's not a guarantee to give me the exam. Unless there's a different way to sort through these individually
Ideally, I'd want the end result to return only one document, where the exam score is the highest:
{
"student_id" : 5,
"class_id" : 30,
"scores" : [
{
"type" : "exam",
"score" : 73.48459944869943
}
]
}
$match student_id condition
$unwind deconstruct scores array
$match type: exam condition
$sort documents by score in descending order
$group by student_id and get first root document
$replaceRoot to replace doc to root
var pipeline = [
{ $match: { student_id: 5 } },
{ $unwind: "$scores" },
{ $match: { "scores.type": "exam" } },
{ $sort: { "scores.score": -1 } },
{
$group: {
_id: "$student_id",
doc: { $first: "$$ROOT" }
}
},
{ $replaceRoot: { newRoot: "$doc" } }
]
Playground
I am watching a tutorial I can understand how this aggregate works, What is the use of pings, $$ROOT in it.
client = pymongo.MongoClient(MY_URL)
pings = client['mflix']['watching_pings']
cursor = pings.aggregate([
{
"$sample": { "size": 50000 }
},
{
"$addFields": {
"dayOfWeek": { "$dayOfWeek": "$ts" },
"hourOfDay": { "$hour": "$ts" }
}
},
{
"$group": { "_id": "$dayOfWeek", "pings": { "$push": "$$ROOT" } }
},
{
"$sort": { "_id": 1 }
}
]);
Let's assume that our collection looks like below:
{
"_id" : ObjectId("b9"),
"key" : 1,
"value" : 20,
"history" : ISODate("2020-05-16T00:00:00Z")
},
{
"_id" : ObjectId("ba"),
"key" : 1,
"value" : 10,
"history" : ISODate("2020-05-13T00:00:00Z")
},
{
"_id" : ObjectId("bb"),
"key" : 3,
"value" : 50,
"history" : ISODate("2020-05-12T00:00:00Z")
},
{
"_id" : ObjectId("bc"),
"key" : 2,
"value" : 0,
"history" : ISODate("2020-05-13T00:00:00Z")
},
{
"_id" : ObjectId("bd"),
"key" : 2,
"value" : 10,
"history" : ISODate("2020-05-16T00:00:00Z")
}
Now based on the history field you want to group and insert the whole documents in to an array field 'items'. Here $$ROOT variable will be helpful.
So, the aggregation query to achieve the above will be:
db.collection.aggregate([{
$group: {
_id: '$history',
items: {$push: '$$ROOT'}
}
}])
It will result in following output:
{
"_id" : ISODate("2020-05-12T00:00:00Z"),
"items" : [
{
"_id" : ObjectId("bb"),
"key" : 3,
"value" : 50,
"history" : ISODate("2020-05-12T00:00:00Z")
}
]
},
{
"_id" : ISODate("2020-05-13T00:00:00Z"),
"items" : [
{
"_id" : ObjectId("ba"),
"key" : 1,
"value" : 10,
"history" : ISODate("2020-05-13T00:00:00Z")
},
{
"_id" : ObjectId("bc"),
"key" : 2,
"value" : 0,
"history" : ISODate("2020-05-13T00:00:00Z")
}
]
},
{
"_id" : ISODate("2020-05-16T00:00:00Z"),
"items" : [
{
"_id" : ObjectId("b9"),
"key" : 1,
"value" : 20,
"history" : ISODate("2020-05-16T00:00:00Z")
},
{
"_id" : ObjectId("bd"),
"key" : 2,
"value" : 10,
"history" : ISODate("2020-05-16T00:00:00Z")
}
]
}
I hope it helps.
I have in MongDb data as below
{
"_id" : 7,
"name" : "Salena Olmos",
"scores" : [
{
"type" : "exam",
"score" : 90.37826509157176
},
{
"type" : "quiz",
"score" : 42.48780666956811
},
{
"type" : "homework",
"score" : 67.18328596625217
},
{
"type" : "homework",
"score" : 96.52986171633331
}
]
}
all I want to sum "scores" for "type" : "homework" as
{ "_id" : 7, "score" : 163.71314768258548}
I have written my query using aggregate and filter condition as below
db.students.aggregate([
{
"$group" :
{
"_id":"$_id",
"score":{$sum: {$filter: {
input: "$scores",
as: "x",
cond: {$eq : ["$$x.type", "homework"]}
}
}
}
}
}
])
but all it gives me as "0" as sum value as :
{ "_id" : 7, "score" : 0 }
Please help me , I am new to MongoDb and trying to learn by solving some exercise problems.
Thanks
You can use below aggregation. Use $let to extract the score from matching scores.
db.students.aggregate({
"$project":{
"score":{
"$sum":{
"$let":{
"vars":{
"mscores":{
"$filter":{
"input":"$scores",
"as":"x",
"cond":{"$eq":["$$x.type","homework"]}
}
}
},
"in":"$$mscores.score"
}
}
}
}
})
I have gone through the MongoDb docs and come up with below solution
db.students.aggregate([
{$unwind: "$scores"},
{$match:{"scores.type" : "homework"}},
{$group : {"_id":"$_id", "score":{$sum: "$scores.score"}}}
])
I have a collection as follows
{ "_id" : 0, "name" : "aimee Zank", "scores" :
[
{ "type" : "exam", "score" : 1.463179736705023 },
{ "type" : "quiz", "score" : 11.78273309957772 },
{ "type" : "homework", "score" : 6.676176060654615}
] }
{"_id" : 1, "name" : "Aurelia Menendez", "scores" :
[
{ "type" : "exam", "score" : 60.06045071030959 },
{ "type" : "quiz", "score" : 52.79790691903873 },
{ "type" : "homework", "score" : 71.761334391544 }
] }
{"_id" : 2, "name" : "Corliss Zuk", "scores" :
[
{ "type" : "exam", "score" : 67.03077096065002 },
{ "type" : "quiz", "score" : 6.301851677835235 },
{ "type" : "homework", "score" : 20.18160621941858}
] }
Now i want the sum of all the scores of each type for respective students
for example for student aimee zank i want the sum of scores for exam+quiz+homework.
I have tried this
db.collection.aggregate(
[
{
$group:
{
_id: "$name",
total: { $sum: "$scores.score" },
}
}
]
)
and this
db.scores.aggregate(
[
{ $project: { name: 1, total: { $add: [ "$scores.score" ] } } }
]
)
But i could not find a solution
Can someone please help me with the query?
After finding no help on stackoverflow and only discouraging people in the group, i have found a solution on my own and it is just one part of the solution of i was searching for:
db.scores.aggregate(
[
{ $unwind : "$scores"},
{ $group:
{
_id: "$name",
total: { $sum: "$scores.score" }
}
}
]
)
I have a collection students look like this:
{
"_id" : 10,
"name" : "Christiano Ronaldo",
"scores" : [
{
"type" : "exam",
"score" : 40.58945534169687
},
{
"type" : "quiz",
"score" : 4.30461571152303
},
{
"type" : "homework",
"score" : 62.36309025722009
},
{
"type" : "homework",
"score" : 32.1707802903173
}
]
}
How do I find out the lowest homework? Using javadriver
Note : I can not change the Data model.
Try this below -
x = db.students.aggregate([{
"$unwind": "$scores"
}, {
"$match": {
"scores.type": "homework"
}
}, {
"$group": {
"_id": "$_id",
"minscore": {
"$min": "$scores.score"
}
}
}])
Your result document "x" contains an array field - lowest scores in the document