unwinding - pairs, triplets ..

[Syd Davenport]

Is there possibility of unwinding based on combinations. For example, I would like to unwind all possible pairs (or triplets etc..) from within an array instead of single element (which is the default behavior).

Thanks

[Kristina Chodorow]

Can you give an example?

[A. Jesse Jiryu Davis]

Consider something like this (for all pairs):

> db.foo.insert({t:[1,2,3]})

> db.foo.aggregate({$project:{s:'$t',t:'$t'}}, {$unwind:'$t'}, {$unwind:'$s'}, {$project:{combination:{0:'$s', 1:'$t'}}})

To do triplets, rename 't' to a third name in the first $project clause, add another $unwind clause, and include the third name in the 'combination' field in the final $project.

On Tuesday, April 17, 2012 9:06:16 AM UTC-4, Syd wrote:

Is there possibility of unwinding based on combinations. For example, I would like to unwind all possible pairs (or triplets etc..) from within an array instead of single element (which is the default behavior).

Thanks

[Syd]

Thanks. This is what I was looking for.

Below code also removes duplicates and same combinations ex. [1,1],
([1,2], [2,1]).

db.foo.aggregate({$project:{s:'$t',t:'$t'}}, {$unwind:'$t'},

{$unwind:'$s'}, {$project:{combination:{0:'$s', 1:'$t', dup: {$cmp:
["$s","$t"] } }}}, {$match: {'combination.dup': {$nin: [0, 1]}}});

[A. Jesse Jiryu Davis]

Nice.

[Syd]

And, doing this crashed our system due to memory outage. We are
reverting back to Pig for this operation.

Are there known performance issues with aggregation framework in the
2.1.1-pre unstable branch? Thanks

[Sam Millman]

I don't know of any personally however I wouldn't use an unstable alpha build to setup something for production, that'd just be a crazy thing to do.

2.1 is mostly for testing only, if you find a bug it's prolly good to JIRA it.

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[A. Jesse Jiryu Davis]

Yes, please do file a ticket at jira.mongodb.org and tell us how to reproduce this error so we can debug it.

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[Chris Westin]

There are some optimizations that haven't made it in yet.  You can see what they are by looking at the open SERVER tickets for component "Aggregation Framework"