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POHow to access MongoDB's aggregation framework from the rmongodb R package
 

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  1. POHow to access MongoDB's aggregation framework from the rmongodb R package
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    <p>I'm trying to access the mongodb aggregation framework from rmongodb. It should be available through mongo.command() but I cannot get the bson correct.</p> <p>Here is a replicable example. In R, set up a test collection:</p> <pre><code>mongo &lt;- mongo.create() db &lt;- "test" ns &lt;- "test.people" buf &lt;- mongo.bson.buffer.create() mongo.bson.buffer.append(buf, "name", "John") mongo.bson.buffer.append(buf, "age", 22L) b &lt;- mongo.bson.from.buffer(buf) mongo.insert(mongo, ns, b); buf &lt;- mongo.bson.buffer.create() mongo.bson.buffer.append(buf, "name", "John") mongo.bson.buffer.append(buf, "age", 35L) b &lt;- mongo.bson.from.buffer(buf) mongo.insert(mongo, ns, b); buf &lt;- mongo.bson.buffer.create() mongo.bson.buffer.append(buf, "name", "Fred") mongo.bson.buffer.append(buf, "age", 27L) b &lt;- mongo.bson.from.buffer(buf) mongo.insert(mongo, ns, b); Now, on the mongo console, the following works: use test db.runCommand({ aggregate : "people", pipeline : [ { $group : { _id : '$name', total : { $sum : 1 } } } ] }) </code></pre> <p>It seems like the following in R would achieve the same effect:</p> <pre><code>mongo.command(mongo, "test", list( aggregate="people", pipeline=list( group=list( "_id"="$name", total=list("$sum"=1) ) ) )) </code></pre> <p>This does not work.</p> <p>For this particular aggregation, I am aware that there are other ways to do it. I'm just providing it as a simple example but I want to get to more complex aggregations in the future.</p> <p>Also, I am aware of another R package for mongodb that I might be able to look into to do the trick, but I'm pretty heavily invested into using this package right now.</p>
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