Couch base map reduce query - mapreduce

Question

I have a 3 Json Documents
Document 1
"No" : 1
"City" : "Patiala"
"Value" : 10
Document 2
"No" : 1
"City" : "Delhi"
"Value" : 11
Document 3
"No" : 1
"City" : "Patiala"
"Value" : 11
I want output like
1 <Delhi or Patiala any one city> 32
I tried query with group level 2
map
function(doc, meta)
{
emit(doc.No,[doc.Value,doc.City]);
}
reduce
function(key,values,rereduce){
if(!rereduce){
var sum=0;
var s=[];
var v=[];
v=values[1];
s=values[0];
for(i=0;i<s.length;++i){
sum+= s[i];
}
return (sum,v[0]);
}else{
var sum=0;
var s=[];
var v;
v=values[1];
s=values[0];
for(i=0;i<s.length;++i){
sum+= s[i];
}
return (sum,v);
}
}
and got the following error
(Reducer: Error building index for view `my_first_view`, reason: TypeError: Cannot read property 'length' of null)
I only want to do group by on 'No' field but display any city.

Answer 1

The CouchDB documentation generally warns against abusing reduce functions by doing this kind of thing, so it's probably worth testing out with datasets of a size you are expecting in production.
You are probably best off using a simple view with the map function you have and a reduce function sum on the doc.Value. Call this twice, once with query params ?reduce=false&key=1&limit=1 and once again with ?group=true&key=1.
Having said all that, and this may kill your performance, this will do what you want in a single query.
Map Function:
function (doc) {
emit(doc.No,[doc.City, doc.Value]);
}
Reduce Function:
function (keys, values, rereduce) {
var city;
var sum = 0;
for (var i = 0; i<values.length; i++){
if (!city){
city = values[i][0];
}
sum = sum + values[i][1];
}
return [city, sum];
}
Query URL:
http://host:5984/db/_design/views/_view/view?group=true&key=1
Gives Result:
{"rows":[
{"key":1,"value":["Patiala",32]}
]}