what is different between mapReduce and aggregation function?

[jamesKim]

what is different between mapReduce and aggregation function?
my example

1.aggregation group function
db.pageviews.group(
{
key: {'user.agent': true},
initial: {sum: 0},
reduce: function(doc, prev) { prev.sum += 1}
});


2.using mapreduce
db.runCommand({mapreduce:"pageviews",......)

when i wanna get a sum propertie. is it different 1. and 2.?

[Nat]

Hi,

 

group command is for basic aggregation where you can't control how to emit the key. The key will be emitted as is as you specify in "key" parameter. mapReduce allows advanced aggregation where you can specify the logic for key emitting. group command is a little bit faster for the same operation (if it can be done using group())