Question

Is there a way in mongo to create user-defined Javascript functions. I have several Map/Reduce functions on the client side that i would like to use within other MR functions.

For example, several MR functions calculate all sorts of averages. I want to be able to use them like so :

function reduce(k,v)
{
    if (val > myDatabaseAverage())
    // ..do something
}

Answer 1

Use

db.system.js.save( { _id : "myDatabaseAverage" , value : function(){
  // ..do something 
} } );

That will store the JS function on the server and can be accessed by m/r from that point on.

For further examples see : mongo/jstests/core/mr_stored.js