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POThis looks like a job for MapReduce...but I just can't figure it out
 

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  1. POThis looks like a job for MapReduce...but I just can't figure it out
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    <p>I've been battling with this for about 2 days now, and any help would be tremendously appreciated. I currently have a very large MongoDB collection(over 100M documents) in the following format:</p> <pre><code>[_id] [date] [score] [meta1] [text1] [text2] [text3] [text4] [meta2] </code></pre> <p>This isn't the exact data in there, I've obfuscated it a little for the purpose of this post, but the schema is identical, and no the format of that data cannot be changed, that's just the way it is.</p> <p>There are a TON of duplicate entries in there, a job is running once a day day adding millions of entries to the database that may have the same data in the text fields but different values for the score, meta1, and meta2 fields. So I need to eliminate the duplicates and shoehorn everything into one collection without duplicate texts:</p> <p>First, I'm going to concatenate the text fields and hash the result, so I have no duplicates containing the same text fields(this part is easy and already works). </p> <p>Here's where I'm struggling: The resulting collection will have an array of each unique meta1, which will in turn be an array containing the dates and scores matching it.</p> <p>So if I have the following three documents in my collection now:</p> <pre><code>[_id] =&gt; random mongoid [date] =&gt; 12092010 [score] =&gt; 3 [meta1] =&gt; somemetadatahere [text1] =&gt; foo [text2] =&gt; bar [text3] =&gt; foo2 [text4] =&gt; bar2 [meta2] =&gt; uniquemeta2data [_id] =&gt; random mongoid [date] =&gt; 12092010 [score] =&gt; 5 [meta1] =&gt; othermetadata [text1] =&gt; foo [text2] =&gt; bar [text3] =&gt; foo2 [text4] =&gt; bar2 [meta2] =&gt; uniquemeta2data1 [_id] =&gt; random mongoid [date] =&gt; 12102010 [score] =&gt; 7 [meta1] =&gt; somemetadatahere (same meta1 as the first document) [text1] =&gt; foo [text2] =&gt; bar [text3] =&gt; foo2 [text4] =&gt; bar2 [meta2] =&gt; uniquemeta2data </code></pre> <p>They should be reduced to this collection(indents are nested documents/arrays). The keys in the datas array come from the values of the meta1 field in the original collection:</p> <pre><code>[_id]=&gt; (md5 hash of all the text fields) [text1] =&gt; foo [text2] =&gt; bar [text3] =&gt; foo2 [text4] =&gt; bar2 [datas] [somemetadatahere] [meta2] =&gt; uniquemeta2data [scores] [12092010]=&gt;3 [12102010]=&gt;7 [othermetadata] [meta2] =&gt; uniquemeta2data1 [scores] [12092010]=&gt;3 </code></pre> <p>This seems like a perfect use case for a MapReduce job, but I'm having trouble wrapping my head around exactly how to do this. </p> <p>Is anyone up for the challenge of helping me figure this out?</p>
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