Question

I have a collection in MongoDb where data in the collection has the following structure :

{userid = 1 (the id of the user), key1 = value1 , key2 = value2, .... }

I want to write mongodb mapreduce functions where i could put the userid in the map function and in the reduce function i need to write they ( key,value ) pairs in a csv (?) file such that they would be :

key1,key2, key3,…

value1,value2,value3,..

value1,value2,value3,..

value1,value2,value3,..

How can i do that with mongodb

Thanks

Answer 1

There is no “file output” option.

The MongoDB documentation has details on exporting data.

In particular, mongoexport allows for export by JSON or CSV which should be legible from other software.

If you want to significantly modify the data output, then you’ll have to use a client library and cursor through the data while writing to a file.