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POCounting documents in MapReduce depending on condition - MongoDB
 

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  1. POCounting documents in MapReduce depending on condition - MongoDB
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    <p>I am trying to use a Map Reduce to count number documents according to one of the field values per date. First, here are the results from a couple of regular find() functions:</p> <pre><code>db.errors.find({ "cDate" : ISODate("2012-11-20T00:00:00Z") }).count(); </code></pre> <p>returns 579 (ie. there are 579 documents for this date)</p> <pre><code>db.errors.find( { $and: [ { "cDate" : ISODate("2012-11-20T00:00:00Z") }, {"Type":"General"} ] } ).count() </code></pre> <p>returns 443 (ie. there are 443 documents for this date where Type="General")</p> <p>Following is my MapReduce:</p> <pre><code>db.runCommand({ mapreduce: "errors", map : function Map() { emit( this.cDate,//Holds a date value { count: 1, countGeneral: 1, Type: this.Type } ); }, reduce : function Reduce(key, values) { var reduced = {count:0,countGeneral:0,Type:''}; values.forEach(function(val) { reduced.count += val.count; if (val.Type === 'General') reduced.countGeneral += val.countGeneral; }); return reduced; }, finalize : function Finalize(key, reduced) { return reduced; }, query : { "cDate" : { "$gte" : ISODate("2012-11-20T00:00:00Z") } }, out : { inline : 1 } }); </code></pre> <p>For the date 20-11-20 the map reduce returns:</p> <pre><code>count: 579 countGeneral: 60 (should be 443 according to the above find query) </code></pre> <p>Now, I understand that the Reduce is unpredictable in the way it loops so how should I do this? Thanks </p>
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    1. USadinas
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    1. COTwo things I immediately see are: You don't need the `$and` in that query, MongoDBs default operator between array elements is `$and` and also in your query to get count you are getting all that equal `ISODate("2012-11-20T00:00:00Z")` but in your MR you are doing a `$gt` as such the two queries counts shouldn't match up. The total count of 579 does though, are you sure your MR is not working correctly?
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      1. POCounting documents in MapReduce depending on condition - MongoDB
      1. USSammaye
    2. COThe `$gte` is Okay since I'm grouping by cDate, the 60 was specifically what was returned for `ISODate("2012-11-20T00:00:00Z")`. there were other numbers for other dates but those are not important since I want to compare to the find query which was done for this date
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      1. USadinas
    3. COOh I saw it as `$gt` not `$gte`, hmm ok, this should count ok, when are you emitting the countGeneral to get the 60 you are?
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      1. USSammaye
 

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