Question

I have a collection of documents like this one:

{
    "_id" : ObjectId("..."),
    "field1": "some string",
    "field2": "another string",
    "field3": 123
}

I’d like to be able to iterate over the entire collection, and find the entire number of fields there are. In this example document there are 3 (I don’t want to include _id), but it ranges from 2 to 50 fields in a document. Ultimately, I’m just looking for the average number of fields per document.

Any ideas?

Answer 1

PRIMARY> var count = 0;
PRIMARY> db.my_table.find().forEach( function(d) { for(f in d) { count++; } });
PRIMARY> count
1074942

This is the most simple way I could figure out how to do this. On really large datasets, it probably makes sense to go the Map-Reduce path. But, while your set is small enough, this’ll do.

This is O(n^2), but I’m not sure there is a better way.