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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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            <title>[SERVER-10205] Group and select the top K elements in each group</title>
                <link>https://jira.mongodb.org/browse/SERVER-10205</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;I would like the ability in the aggregation framework to group and select the top K elements in each group.&lt;/p&gt;

&lt;p&gt;Here is an example:&lt;/p&gt;

&lt;p&gt;Let&apos;s say I have documents with the following structure:&lt;/p&gt;

{ &quot;_id&quot;:..., &quot;Group&quot;: 1, &quot;Value&quot;: 4 }
{ &quot;_id&quot;:..., &quot;Group&quot;: 2, &quot;Value&quot;: 8 }
{ &quot;_id&quot;:..., &quot;Group&quot;: 1, &quot;Value&quot;: 10 }

&lt;p&gt;Given X, Y and K, I would like to be able to use the aggregation framework to do the following:&lt;/p&gt;

&lt;ul class=&quot;alternate&quot; type=&quot;square&quot;&gt;
	&lt;li&gt;Select all documents with the &quot;Group&quot; property between X and Y&lt;/li&gt;
	&lt;li&gt;Group by the &quot;Group&quot; property&lt;/li&gt;
	&lt;li&gt;In each group: pick only the K documents with the largest &quot;Value&quot; property&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;Because K will be much smaller than the size of the collection itself, I would like to be able to do that in a way that is memory efficient.&lt;/p&gt;

&lt;p&gt;There is a new feature in 2.4 where we can efficiently sort then limit with the aggregation framework. This is basically the same thing, working on groups.&lt;/p&gt;

&lt;p&gt;I have no preference on which operator should enable this scenario, as long as it is possible to achieve what I just described.&lt;/p&gt;</description>
                <environment>All</environment>
        <key id="82259">SERVER-10205</key>
            <summary>Group and select the top K elements in each group</summary>
                <type id="2" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14711&amp;avatarType=issuetype">New Feature</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="3">Duplicate</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="flavien">Flavien</reporter>
                        <labels>
                    </labels>
                <created>Mon, 15 Jul 2013 11:10:07 +0000</created>
                <updated>Wed, 10 Dec 2014 23:04:26 +0000</updated>
                            <resolved>Wed, 24 Jul 2013 06:42:54 +0000</resolved>
                                                                    <component>Aggregation Framework</component>
                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="387580" author="asya" created="Wed, 24 Jul 2013 06:42:54 +0000"  >&lt;p&gt;Duplicate of &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-9377&quot; title=&quot;Allow collecting &amp;quot;top&amp;quot; N values for each group&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-9377&quot;&gt;&lt;del&gt;SERVER-9377&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
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