So I have data that looks like this:
{
_id: 1,
ranking: 5,
tags: ['Good service', 'Clean room']
}
Each of these stand for a review. There can be multiple reviews with a ranking of 5. The tags field can be filled with up to 4 different tags.
4 tags are: 'Good service', 'Good food', 'Clean room', 'Need improvement'
I want to make a MongoDB aggregate query where I say 'for each ranking (1-5) give me the number of times each tag occurred for each ranking.
So an example result might look like this, _id being the ranking:
[
{ _id: 5,
totalCount: 5,
tags: {
goodService: 1,
goodFood: 3,
cleanRoom: 1,
needImprovement: 0
},
{ _id: 4,
totalCount: 7,
tags: {
goodService: 0,
goodFood: 2,
cleanRoom: 3,
needImprovement: 0
},
...
]
Having trouble with the counting the occurrences of each tag. Any help would be appreciated
You can try below aggregation.
db.colname.aggregate([
{"$unwind":"$tags"},
{"$group":{
"_id":{
"ranking":"$ranking",
"tags":"$tags"
},
"count":{"$sum":1}
}},
{"$group":{
"_id":"$_id.ranking",
"totalCount":{"$sum":"$count"},
"tags":{"$push":{"tags":"$_id.tags","count":"$count"}}
}}
])
To get the key value pair instead of array you can replace $push with $mergeObjects from 3.6 version.
"tags":{"$mergeObjects":{"$arrayToObject":[[["$_id.tags","$count"]]]}}
Related
I am new to Mongo. Posting this question because i am not sure how to search this on google
i have a book documents like below
{
bookId: 1
title: 'some title',
publicationDate: DD-MM-YYYY,
editions: [{
editionId: 1
},{
editionId: 2
}]
}
and another one like this
{
bookId: 2
title: 'some title 2',
publicationDate: DD-MM-YYYY,
editions: [{
editionId: 1
},{
editionId: 1
}]
}
I want to write a query db.books.find({}) which would return only those books where editions.editionId has been duplicated for a book.
So in this example, for bookId: 2 there are two editions with the editionId:1.
Any suggestions?
You can use the aggregation framework; specifically, you can use the $group operator to group the records together by book and edition id, and count how many times they occur : if the count is greater than 1, then you've found a duplication.
Here is an example:
db.books.aggregate([
{$unwind: "$editions"},
{$group: {"_id": {"_id": "$_id", "editionId": "$editions.editionId"}, "count": {$sum: 1}}},
{$match: {"count" : {"$gt": 1}}}
])
Note that this does not return the entire book records, but it does return their identifiers; you can then use these in a subsequent query to fetch the entire records, or do some de-duplication for example.
I have two documents in one collection.
{id: 1, list_data: [1, 2, 4, 5]}
{id: 1, list_data: [2, 5, 8, 9]}
I want merge those data into one document.
{id: 1, list_data: [1, 2, 4, 5, 8, 9]}
How can I do this job?
Please help me.
Thanks.
According to MongoDB documentation
Aggregation operations group values from multiple documents together,
and can perform a variety of operations on the grouped data to return
a single result.
Please refer the aggregation query as mentioned below .
db.collection.aggregate(
// Pipeline
[
// Stage 1
{
$unwind: {
path:'$list_data'
}
},
// Stage 2
{
$group: {
_id:{id:'$id'},
list_data:{$addToSet:'$list_data'}
}
},
// Stage 3
{
$project: {
'_id.id':1,
"list_data":1
}
},
]
);
In above query document is processed through multiple stages of aggregation pipeline
Say that I have a document:
{ _id: 1, item: "ABC", supplier: "XYZ", price: 10, available: 23 }
and then I run something like
db.products.update(
{ _id: 1, supplier: "XYZ" },
{ stock_value: {$mul: ["price", "available", 0.8] }}
)
to get a document
{ _id: 1, item: "ABC", supplier: "XYZ", price: 10, available: 23, stock_value: 184 }
I'd like to do this without loading everything into the client. And I need to be able to specify a different constant (e.g. the 0.8) for each supplier.
I'm thinking I should just use an aggregation with an $out to the same collection, to overwrite the whole then when the update is done, but I can't do a different aggregate() call for each supplier since I'm overwriting the collection - all other suppliers will be skipped. Is there some sort of "in place" aggregation? or a way to append $out ?
Suppose, I have the following database:
{
_id: 1,
name: 'Alice',
courses: [
{
_id: 'DB103',
credits: 6
},
{
_id: 'ML203',
credits: 4
}
]
},
{
_id: 2,
name: 'Bob',
courses: []
}
I now want to 'upsert' the document with the course id 'DB103' in both documents. Although the _id field should remain the same, the credits field value should change (i.e. to 4). In the first document, the respective field should be changed, in the second one, {_id: 'DB103', credits: 4} should be inserted into the courses array.
Is there any possibility in MongoDB to handle both cases?
Sure, I could search with $elemMatch in courses for 'DB103' and if I haven't found it, insert, otherwise update the value. But these are two steps and I would like to do both in just one.
Suppose I have the following data:
{_id: 1, tags: ['foo', 'bar']}
{_id: 2, tags: ['bar',]}
{_id: 3, tags: ['foo',]}
{_id: 4, tags: ['bar', 'foo']}
{_id: 5, tags: ['foo']}
I would like a query to return the number of times each tag is used. In this case the tag "foo" was used 4 times and "bar" was used 3 times. I'm guessing the aggregate functions would help me here but not sure how. Please help me with an example!
Thanks gurus!
Figured it out :)
db.test.aggregate({$unwind: "$tags"}, {$group: {_id: "$tags", total: { $sum: 1 }}});
I wouldn't mind if someone knew a more efficient way though :)