map reduce example

mr.js

// groups users by type
var map = function() {
        emit(this.type, 1)
}
var reduce = function(key, values) {
        var result = 0
        values.forEach(function(value) {
                result += value
        })
        return result
}
var options = {out:{inline:1}}
db.users.mapReduce(map, reduce, options)