小编Kas*_*sen的帖子

我正在尝试进行PyMongo聚合-数组的$ group平均值，但找不到与我的问题匹配的任何示例。

资料范例

{
    Subject: "Dave",
    Strength: [1,2,3,4]
},
{
    Subject: "Dave",
    Strength: [1,2,3,5]
},
{
    Subject: "Dave",
    Strength: [1,2,3,6]
},
{
    Subject: "Stuart",
    Strength: [4,5,6,7]
},
{
    Subject: "Stuart",
    Strength: [6,5,6,7]
},
{
    Subject: "Kevin",
    Strength: [1,2,3,4]
},
{
    Subject: "Kevin",
    Strength: [9,4,3,4]
}

想要的结果

{
    Subject: "Dave",
    mean_strength = [1,2,3,5]
},
{
    Subject: "Stuart",
    mean_strength = [5,5,6,7]
},
{
    Subject: "Kevin",
    mean_strength = [5,3,3,4]
}

我已经尝试过这种方法，但是MongoDB会将数组解释为Null吗？

pipe = [{'$group': {'_id': 'Subject', 'mean_strength': {'$avg': '$Strength'}}}]
results = db.Walk.aggregate(pipeline=pipe)

Out: …