$floor (aggregation)

Definition定义

$floor

Returns the largest integer less than or equal to the specified number.返回小于或等于指定数字的最大整数。

$floor has the following syntax:语法如下：

{ $floor: <number> }

The <number> expression can be any valid expression as long as it resolves to a number. <number>表达式可以是任何有效的表达式，只要它解析为数字。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

If the argument resolves to a value of null or refers to a field that is missing, $floor returns null. 如果参数解析为null值或引用缺少的字段，$floor将返回null。If the argument resolves to NaN, $floor returns NaN.如果参数解析为NaN，则$floor返回NaN。

Example示例

A collection named samples contains the following documents:名为samples的集合包含以下文档：

{ _id: 1, value: 9.25 }
{ _id: 2, value: 8.73 }
{ _id: 3, value: 4.32 }
{ _id: 4, value: -5.34 }

The following example returns both the original value and the floor value:以下示例同时返回原始值和下限值：

db.samples.aggregate([
   { $project: { value: 1, floorValue: { $floor: "$value" } } }
])

The operation returns the following results:该操作返回以下结果：

{ "_id" : 1, "value" : 9.25, "floorValue" : 9 }
{ "_id" : 2, "value" : 8.73, "floorValue" : 8 }
{ "_id" : 3, "value" : 4.32, "floorValue" : 4 }
{ "_id" : 4, "value" : -5.34, "floorValue" : -6 }