如何将数字截断为 3 位小数 [英] How to truncate a number to 3 decimals

问题描述

我不知道如何在 MongoDB 中舍入一个数字.我只找到了如何使用 2 个小数但没有找到更多小数的方法.

I do not know how to round a number in MongoDB. I only find how to do it with 2 decimals but not with more decimals.

"location" : {
    "type" : "Point",
    "coordinates" : [ 
        -74.00568, 
        40.70511
    ]
}

这些是我需要在点后用 3 个数字四舍五入的坐标示例.谢谢

These is an example of a coordinate that I need to round with 3 numbers after the dot. Thank you

推荐答案

对于 3 位小数四舍五入，您可以使用此公式.

For 3 decimal rounding, you can use this formula.

$divide: [ {$trunc: { $multiply: [ "$$coordinate" , 1000 ] } }, 1000 ]

例如，使用您的示例数据，并使用此聚合:

For example, with your sample data, and using this aggregation:

db.getCollection('Test2').aggregate([
    { $project : 
        { 
            "location.type" : "$location.type",
            "location.coordinates" :  
            { 
                $map: 
                {
                    input: "$location.coordinates",
                    as: "coordinate",
                    in: { $divide: [ {$trunc: { $multiply: [ "$$coordinate" , 1000 ] } }, 1000 ] }
              }
            }   
        } 
    }
])

你可以获得想要的结果.

you can obtain the desired result.

{
    "_id" : ObjectId("59f9a4c814167b414f6eb553"),
    "location" : {
        "type" : "Point",
        "coordinates" : [ 
            -74.005, 
            40.705
        ]
    }
}

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