$filter
The $filter operator filters for elements from an array based on a specified condition.
$filter
The $filter operator is used to filter elements from an array based on a specified condition. This operator is useful when you need to manipulate or retrieve specific array elements within documents.
Parameters
| Parameter | Description |
|---|---|
input | An expression that resolves to an array. |
as | A string that specifies the variable name for each element in the input array. |
cond | An expression that determines whether to include the element in the output array. |
Examples
Consider this sample document from the stores collection.
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
"location": {
"lat": 60.1441,
"lon": -141.5012
},
"staff": {
"totalStaff": {
"fullTime": 2,
"partTime": 0
}
},
"sales": {
"salesByCategory": [
{
"categoryName": "DJ Headphones",
"totalSales": 35921
},
{
"categoryName": "DJ Cables",
"totalSales": 1000
}
],
"fullSales": 3700
},
"promotionEvents": [
{
"eventName": "Bargain Blitz Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 3,
"Day": 11
},
"endDate": {
"Year": 2024,
"Month": 2,
"Day": 18
}
},
"discounts": [
{
"categoryName": "DJ Turntables",
"discountPercentage": 18
},
{
"categoryName": "DJ Mixers",
"discountPercentage": 15
}
]
},
{
"eventName": "Discount Delight Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 5,
"Day": 11
},
"endDate": {
"Year": 2024,
"Month": 5,
"Day": 18
}
}
}
],
"tag": [
"#ShopLocal",
"#FashionStore",
"#SeasonalSale",
"#FreeShipping",
"#MembershipDeals"
]
}Example 1: Retrieve an element filtered on condition
This query demonstrates how to filter sales category based on totalSales.
db.stores.aggregate([{
$match: {
_id: "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5"
}
},
{
$project: {
filteredSalesByCategory: {
$filter: {
input: "$sales.salesByCategory",
as: "item",
cond: {
$gt: ["$$item.totalSales", 10000]
}
}
}
}
}
])This query returns the following result.
[
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"filteredSalesByCategory": [
{
"categoryName": "DJ Headphones",
"totalSales": 35921
}
]
}
]