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- $trunc (aggregation)
$trunc (aggregation)¶
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Definition¶
- $trunc¶
3.2 新版功能.
Truncates a number to its integer.
$trunc has the following syntax:
{ $trunc: <number> }
The <number> expression can be any valid expression as long as it resolves to a number. For more information on expressions, see Expressions.
Behavior¶
If the argument resolves to a value of null or refers to a field that is missing, $trunc returns null. If the argument resolves to NaN, $trunc returns NaN.
| Example | Results |
|---|---|
| { $trunc: 0 } | 0 |
| { $trunc: 7.80 } | 7 |
| { $trunc: -2.3 } | -2 |
Example¶
A collection named samples contains the following documents:
{ _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 truncated value:
db.samples.aggregate([
{ $project: { value: 1, truncatedValue: { $trunc: "$value" } } }
])
The operation returns the following results:
{ "_id" : 1, "value" : 9.25, "truncatedValue" : 9 }
{ "_id" : 2, "value" : 8.73, "truncatedValue" : 8 }
{ "_id" : 3, "value" : 4.32, "truncatedValue" : 4 }
{ "_id" : 4, "value" : -5.34, "truncatedValue" : -5 }