Write mongodb mapReduce result to a file

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.

Answer 2

You can not write data to a file directly. You have to implement such a functionality on the application level by reading the data from the collection and writing it to the filesystem in whatever format.