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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-9334] Aggregation framework - operator for adding vectors/array</title>
                <link>https://jira.mongodb.org/browse/SERVER-9334</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;It would be very useful to be able to do operations on arrays as if they were vectors, in particular to add them.  So this would add the 0th entry of the arrays in the pipeline and then the 1st, 2nd, etc.  The result will be one document with an array with each entry being the sum of all the items in that same position in the source documents.  &lt;/p&gt;

&lt;p&gt;This can be useful in doing risk calculations in financial services.  &lt;/p&gt;

&lt;p&gt;This could be done today with unwinding which doesn&apos;t perform as well as this would.  &lt;/p&gt;</description>
                <environment></environment>
        <key id="71561">SERVER-9334</key>
            <summary>Aggregation framework - operator for adding vectors/array</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="9">Done</resolution>
                                        <assignee username="backlog-server-query">Backlog - Query Team</assignee>
                                    <reporter username="matt.kalan@mongodb.com">Matt Kalan</reporter>
                        <labels>
                            <label>expression</label>
                    </labels>
                <created>Thu, 11 Apr 2013 21:48:04 +0000</created>
                <updated>Tue, 6 Dec 2022 05:22:03 +0000</updated>
                            <resolved>Wed, 13 Sep 2017 15:25:57 +0000</resolved>
                                                    <fixVersion>3.4.0</fixVersion>
                                    <component>Aggregation Framework</component>
                                        <votes>4</votes>
                                    <watches>7</watches>
                                                                                                                <comments>
                            <comment id="1671914" author="asya" created="Wed, 13 Sep 2017 15:25:57 +0000"  >&lt;p&gt;This is possible as of 3.4 with something like the following to sum to arrays &quot;a&quot; and &quot;b&quot;:&lt;/p&gt;

&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;db.c.aggregate({$addFields:{sum:{$map:{input:{$zip:{inputs:[&quot;$a&quot;,&quot;$b&quot;]}}, in:{ $sum:&quot;$$this&quot;}}}}})&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;{ &quot;_id&quot; : ObjectId(&quot;59b94d010d66cc8714ea5f40&quot;), &quot;a&quot; : [ 1, 2, 3 ], &quot;b&quot; : [ 11, 12, 13 ], &quot;sum&quot; : [ 12, 14, 16 ] }&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;</comment>
                            <comment id="1468795" author="asya" created="Wed, 4 Jan 2017 00:52:25 +0000"  >&lt;p&gt;Correct - you can use $zip options useLongestLength and defaults to take care of arrays (vectors) being of different length and to provide default value to $add in that case.&lt;/p&gt;

&lt;p&gt;You would only use $reduce if you needed to sum all of the arrays - I think you&apos;re looking for $map and $sum where $zip produces the &quot;input&quot; to $map.  See first example here: &lt;a href=&quot;http://www.kamsky.org/stupid-tricks-with-mongodb/using-34-aggregation-enhancements-for-parallel-array-processing&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;http://www.kamsky.org/stupid-tricks-with-mongodb/using-34-aggregation-enhancements-for-parallel-array-processing&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="1468527" author="matt.kalan@10gen.com" created="Tue, 3 Jan 2017 20:03:17 +0000"  >&lt;p&gt;To confirm, you would do a $zip passed to $reduce with $add to add the 2 original vectors, correct? I&apos;m not sure how we process it but that could be two passes of the vectors instead of merging them in one pass&lt;/p&gt;</comment>
                            <comment id="1468461" author="asya" created="Tue, 3 Jan 2017 19:14:54 +0000"  >&lt;p&gt;Now that 3.4 has $zip expression for parallel array processing, can this ticket be closed?&lt;/p&gt;</comment>
                    </comments>
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            <issuekey id="88454">SERVER-10676</issuekey>
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