how to unwind in map/reduce

[Vishnu Viswanath]

Hi

I have a doc with array of elements,

I would like to do map/reduce after unwinding the doc. how can i do this?

Thanks

[Stephen Steneker]

On Sunday, 26 January 2014 06:44:56 UTC+11, Vishnu Viswanath wrote:

I have a doc with array of elements,

I would like to do map/reduce after unwinding the doc. how can i do this?

Hi Vishnu,

If you want to unwind arrays in Map/Reduce, you can iterate the array(s) in your map() function and emit multiple values for the same document.

Here is an example in the MongoDB manual using a "for" loop:

 http://docs.mongodb.org/manual/tutorial/map-reduce-examples/#calculate-order-and-total-quantity-with-average-quantity-per-item

Depending on the aggregation result you are trying to achieve, you may find it easier and more performant to write your query in the Aggregation Framework rather than Map/Reduce:

  http://docs.mongodb.org/manual/reference/operator/aggregation/unwind/

Regards,

Stephen