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POMongodb Aggregation Framework | Group over multiple values?
 

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    <p>I would like to use mongoDB's Aggregation Framework to run what in SQL would look a bit like:</p> <pre><code>SELECT SUM(A), B, C from myTable GROUP BY B, C; </code></pre> <p>The docs state:</p> <blockquote> <p>You can specify a single field from the documents in the pipeline, a previously computed value, or an aggregate key made up from several incoming fields.</p> </blockquote> <p>But it's unclear what 'an aggregate key made from several incoming fields' actually is?</p> <p>My dataset is a bit like this:</p> <pre><code>[{ "timeStamp" : 1341834988666, "label" : "sharon", "responseCode" : "200", "value" : 10, "success" : "true"}, { "timeStamp" : 1341834988676, "label" : "paul", "responseCode" : "200", "value" : 60, "success" : "true"}, { "timeStamp" : 1341834988686, "label" : "paul", "responseCode" : "404", "value" : 15, "success" : "true"}, { "timeStamp" : 1341834988696, "label" : "sharon", "responseCode" : "200", "value" : 35, "success" : "false"}, { "timeStamp" : 1341834988166, "label" : "paul", "responseCode" : "200", "value" : 40, "success" : "true"}, { "timeStamp" : 1341834988266, "label" : "paul", "responseCode" : "404", "value" : 99, "success" : "false"}] </code></pre> <p>My query looks like this:</p> <pre><code>resultsCollection.aggregate( { $match : { testid : testid} }, { $skip : alreadyRead }, { $project : { timeStamp : 1 , label : 1, responseCode : 1 , value : 1, success : 1 }}, { $group : { _id : "$label", max_timeStamp : { $timeStamp : 1 }, count_responseCode : { $sum : 1 }, avg_value : { $sum : "$value" }, count_success : { $sum : 1 } }}, { $group : { ? }} ); </code></pre> <p>My instinct was to try to pipe the results through to a second group, I know you can do this but it won't work because the first group already reduces the dataset too much and the required level of detail is lost.</p> <p>What I want to do is group using <code>label</code>, <code>responseCode</code> and <code>success</code> and get the sum of value from the result. It should look a bit like:</p> <pre><code>label | code | success | sum_of_values | count sharon | 200 | true | 10 | 1 sharon | 200 | false | 35 | 1 paul | 200 | true | 100 | 2 paul | 404 | true | 15 | 1 paul | 404 | false | 99 | 1 </code></pre> <p>Where there are five groups:</p> <pre><code>1. { "timeStamp" : 1341834988666, "label" : "sharon", "responseCode" : "200", "value" : 10, "success" : "true"} 2. { "timeStamp" : 1341834988696, "label" : "sharon", "responseCode" : "200", "value" : 35, "success" : "false"} 3. { "timeStamp" : 1341834988676, "label" : "paul", "responseCode" : "200", "value" : 60, "success" : "true"} { "timeStamp" : 1341834988166, "label" : "paul", "responseCode" : "200", "value" : 40, "success" : "true"} 4. { "timeStamp" : 1341834988686, "label" : "paul", "responseCode" : "404", "value" : 15, "success" : "true"} 5. { "timeStamp" : 1341834988266, "label" : "paul", "responseCode" : "404", "value" : 99, "success" : "false"} </code></pre>
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