组结果中的MongoDB max [英] MongoDB max in group results

问题描述

我将结果按 mvid 分组，并将每个组中出现的次数进行了计数。

I grouped results by mvid and the counted number of occurrences in each group.

db.some_details.aggregate([
{$group: {_id: "$mvid", count: {$sum: 1}}}
])

现在，我想选择最大计数的组。这是我的天真猜测：

Now, I would like to select group with max count. Here is my naive guess:

db.some_details.aggregate([
{$group: {_id: "$mvid", count: {$sum: 1}}},
{$max: "count"}
])

显然，它会产生错误。我需要将max与group一起使用，但是我没有什么可以分组的。

It, obviously, generates an error. I need to use max with group, but I don't have anything to group on.

推荐答案

可行的方法是对结果进行排序，然后仅使用第一个元素：

What also would work is sorting the result and then using only the first element:

db.some_details.aggregate([
{$group: {_id: "$mvid", count: {$sum: 1}}},
{$sort: {"count": -1}},
{$limit: 1 }
])

与chridam的解决方案相比，我看到的优点是，您还可以得到具有最大数量的组的ID，但我希望它的速度较慢（未经测试）。

The advantage that I see compared to chridam's solution is that you also get the id of the group with the maximum count, but I expect it to be slower (not tested).

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