javascript - Trouble Pivoting data with Map Reduce -

i having trouble pivoting dataset map reduce. i've been using mongodb cookbook help, i'm getting weird errors. want take below collection , pivot each user has list of of review ratings.

my collection looks this:

{   'type': 'review',   'business_id': (encrypted business id),   'user_id': (encrypted user id),   'stars': (star rating),   'text': (review text), } 

map function (wrapped in python):

map = code("""" function(){ key = {user : this.user_id}; value = {ratings: [this.business_id, this.stars]};  emit(key, value); } """) 

the map function should return array of values associated key... reduce function (wrapped in python):

reduce = code(""" function(key, values){ var result = { value: [] }; temp = [];  (var = 0; < values.length; i++){ temp.push(values[i].ratings); } result.value = temp; return result; } """) 

however, results return one less rating total. in fact, users have none returned, can't happen. entries following:

{u'_id': {u'user: u'zwzytzniayfoqveg8xcvxw'}, u'value': [none, [u'e9nn4xxjdhj4qtkcopq_vg', 3.0], none, [...]...] 

i can't pinpoint in code causing this. if there 3 reviews, have business ids , ratings in document. plus, using 'values.length + 1' in loop condition breaks values[i] reason.

edit 1

i've embraced fact reduce gets called multiple times on itself, below new reducer. returns array of [business, rating, business, rating]. idea how output [business, rating] arrays instead of 1 giant array?

function(key, value){ var result = { ratings:[] }; var temp = []; values.foreach(function(value){     value.ratings.foreach(function(rating){         if(temp.indexof(rating) == -1){             temp.push(rating);         }     }); });  result. rartings = temp; return result; } 

heres test example:

1) add sample data:

db.test.drop(); db.test.insert(   [{     'type': 'review',     'business_id': 1,     'user_id': 1,     'stars': 1,   },   {     'type': 'review',     'business_id': 2,     'user_id': 1,     'stars': 2,   },   {     'type': 'review',     'business_id': 2,     'user_id': 2,     'stars': 3,   }] ); 

2) map function

var map = function() {   emit(this.user_id, [[this.business_id, this.stars]]); }; 

here set results want them @ end of process. why? because if there ever single review user (the key grouping by) results won't go through reduce phase.

3) reduce function

var reduce = function(key, values) {   var result = { ratings: [] };   values.foreach(function(value){     result.ratings.push(value[0]);   });    return result; }; 

here collect values, remembering nested them in map method, can pick out first value each set of results.

4) run map reduce:

db.test.mapreduce(map, reduce, {finalize: final, out: { inline: 1 }}); 

alternative - use aggregation framework:

db.test.aggregate({   $group: {     _id: "$user_id",      ratings: {$addtoset: {business_id: "$business_id", stars: "$stars"}}   } });