MongoDB: Combine data from multiple collections into one..how?

Question

How can I (in MongoDB) combine data from multiple collections into one collection?

Can I use map-reduce and if so then how?

I would greatly appreciate some

Answer 1

Mongorestore has this feature of appending on top of whatever is already in the database, so this behavior could be used for combining two collections:

1. mongodump collection1
2. collection2.rename(collection1)
3. mongorestore

Didn't try it yet, but it might perform faster than the map/reduce approach.