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how to get array of fields in mongo aggregate

I am using a Mongo aggregated framework, suppose if I am having collection structure like this
{
{
_id: ObjectId(123)
name: john,
sessionDuration: 29
},
{
_id: ObjectId(456)
name: moore,
sessionDuration: 45
},
{
_id: ObjectId(789)
name: cary,
sessionDuration: 25
},
}
I want to query and create a pipeline such that it return something like this:
{
durationsArr: [29, 49, 25, '$sessionDuration_Field_From_Document' ];
}
I am doing this because I want to get average of durations from all the documents, so first adding all of it into an array, then I will add last stage where I do the $avg operation.
Any idea of how can I get the array of sessionDurationField. or do you have any other best approach to calculate the sessionDuration Average from the collection? please thoroughly explain am new to mongo aggregation.

$group - Group all documents.
1.1. $avg - Calculate the average of sessionDuration for all documents.
db.collection.aggregate([
{
$group: {
_id: null,
avgSessionDuration: {
$avg: "$sessionDuration"
}
}
}
])
Demo # Mongo Playground

how to $bucket only for unique document based on some field

I am using a Mongo aggregated framework, suppose if I am having collection structure like this
{
{
_id: ObjectId(123)
name: john,
sessionDuration: 29
},
{
_id: ObjectId(456)
name: moore,
sessionDuration: 45
},
{
_id: ObjectId(789)
name: john,
sessionDuration: 25
},
{
_id: ObjectId(910)
name: john,
sessionDuration: 45
},
etc...
}
user with the same name is the one who is using different sessions like in the following example: John is using service from three device with 3 sessions durations are: 2 less than 30 (29,25) and 1 less than 50(45).
I want to do a bucket query for boundaries [0,30,50] but in the range it must only count the user with a unique names, no same name user with less than 30 or 50 duration count more than one, means the result should look like this
{
time: Unique_Name_Users_Only_Lies_In_This_Boundary,
‘30’: 1,
‘50’: 2,
}
so john was having 2 sessions less than 30 duration so we only need 1 from these two.
What I tried:
I group all the docs first with unique name only, then apply bucket. but this approach will also skip the john with 45 sessionDuration.
How can I only get the unique name document count in a particular duration of $bucket boundary?

One option is to use the $bucket with $addToSet and then use $group with $arrayToObject to get your formatting:
db.collection.aggregate([
{$bucket: {
groupBy: "$sessionDuration",
boundaries: [0, 30, 50],
default: "Other",
output: {res: {$addToSet: "$name"}}
}},
{$group: {
_id: 0,
res: {$push: {k: {$toString: "$_id"}, v: {$size: "$res"}}}
}},
{$replaceRoot: {newRoot: {$arrayToObject: "$res"}}}
])
See how it works on the playground example
Notice that the _id of a bucket is its lower boundary. You can manipulate this if you really want, but I don't recommend it

Mongoose get all documents matching array intersection

By array intersection I mean, the inventory has a lot more elements than each document ingredients array, and the result I want to get from the query is all documents which all array elements are contained within the inventory. $all will get me zero results since the inventory has more elements than can be found in ingredients even if all ingredients are found within the inventory,
I have thousands of docs that have an array field of strings
{
...
recipe: "recipe1",
ingredients: [ "1 cup cooked quinoa", "6 tbsp butter", "1 large egg" ]
...
},
{
...
recipe: "recipe2",
ingredients: [ "2 lemons", "2 tbsp butter", "1 large egg" ]
...
}
{
...
recipe: "recipe3",
ingredients: [ "1lb salmon", "1 pinch pepper", "4 spears asparagus" ]
...
}
and I'm trying to find all documents where all elements in the ingredients array are contained in a sample array that contains lots of elements, lets say for the case this only contains this:
inventory = [ "lemons", "butter", "egg", "milk", "bread", "salmon", "asparagus", "pepper" ]
With this inventory array, I want to get recipe2 and recipe3.
Right now I have this inventory array and query (thanks to turivishal):
let inventory = ["lemons", "butter", "egg", "milk", "bread", "salmon", "asparagus", "pepper"];
inventory = inventory.map((i) => new RegExp(i, "i"));
query:
Recipe.find({
ingredients: { $all: inventory }
})
Expected result:
{
...
recipe: "recipe2",
ingredients: [ "2 lemons", "2 tbsp butter", "1 large egg" ]
...
}
{
...
recipe: "recipe3",
ingredients: [ "1lb salmon", "1 pinch pepper", "4 spears asparagus" ]
...
}
But I'm getting zero results

You can try aggregation operator in mquery using $expr expression condition,
first of all you can join the array of string by | order symbol and make a string, and use it in $regex search,
$filter to iterate loop of ingredients
$regexMatch to match element has any matching word
$size to get the total size of filtered elements
$eq to match filtered result and actual ingredients is equal
let inventory = ["lemons", "butter", "egg", "milk", "bread", "salmon", "asparagus", "pepper"];
let inventoryStr = inventory.join("|");
// "lemons|butter|egg|milk|bread|salmon|asparagus|pepper"
Recipe.find({
$expr: {
$eq: [
{
$size: {
$filter: {
input: "$ingredients",
cond: {
$regexMatch: {
input: "$$this",
regex: inventoryStr,
options: "i"
}
}
}
}
},
{ $size: "$ingredients" }
]
}
})
Playground

How to implement multi level sorting in javascript using lodash?

The problem :
A job board with filter system where the users can set tags preference.
I need to sort the list of jobs based on the number of tags being matched, multiple jobs can have the same tag count and then I have to sort the most recent job within each tag count group.
My approach right now : I group the jobs based on their tag match count. I neglect the ones which have zero count. I proceed to sort each group with their date in descending order.
Finally merge the collections in the descending order of tag count.
Is there a better of doing this in lodash or plain javascript using functional programming like reduce, map, filter.
DateA < DateB < Date C and so on...
Input:
[
{ tagCount: 2, date: DateA},
{ tagCount: 2, date: DateB},
{ tagCount: 1, date: DateC},
{ tagCount: 3, date: DateD},
]
Output:
[
{ tagCount: 3, date: DateD},
{ tagCount: 2, date: DateB},
{ tagCount: 2, date: DateA},
{ tagCount: 1, date: DateC}
]

You can use _.orderBy() and state ['tagCount', 'date'] as the sorting properties, and ['desc', 'desc'] as the respective sort order for each of them:
the desc as the sort order:
const input = [{ tagCount: 2, date: 'DateA'}, { tagCount: 2, date: 'DateB'}, { tagCount: 1, date: 'DateC'}, { tagCount: 3, date: 'DateD'}]
const result = _.orderBy(input, ['tagCount', 'date'], ['desc', 'desc'])
console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.20/lodash.min.js" integrity="sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww==" crossorigin="anonymous"></script>

Is it possible to find random documents in collection, without same fields? (monogdb\node.js)

For example, I have a collection users with the following structure:
{
_id: 1,
name: "John",
from: "Amsterdam"
},
{
_id: 2,
name: "John",
from: "Boston"
},
{
_id: 3,
name: "Mia",
from: "Paris"
},
{
_id: 4,
name: "Kate",
from: "London"
},
{
_id: 5,
name: "Kate",
from: "Moscow"
}
How can I get 3 random documents in which names will not be repeated?
Using the function getFourNumbers(1, 5), I get array with 3 non-repeating numbers and search by _id
var random_nums = getThreeNumbersnumbers(1, 5); // [2,3,1]
users.find({_id: {$in: random_nums}, function (err, data) {...} //[John, Mia, John]
But it can consist two Johns or two Kates, what is unwanted behavior. How can I get three random documents ( [John, Mia, Kate]. Not [John, Kate, Kate] or [John, Mia, John]) with 1 or maximum 2 queries? Kate or John (duplicated names) should be random, but should not be repeated.

There you go - see the comments in the code for further explanation of what the stages do:
users.aggregate(
[
{ // eliminate duplicates based on "name" field and keep track of first document of each group
$group: {
"_id": "$name",
"doc": { $first: "$$ROOT" }
}
},
{
// restore the original document structure
$replaceRoot: {
newRoot: "$doc"
}
},
{
// select 3 random documents from the result
$sample: {
size:3
}
}
])
As always with the aggrgation framework you can run the query with more or less stages added in order to see the transformations step by step.

I think what you are looking for is the $group aggregator, which will give you the distinct value of the collection. It can be used as:
db.users.aggregate( [ { $group : { name : "$name" } } ] );
MongoDB docs: Retrieve Distinct Values