MongoDB - reduce function does not work properly - mongodb

Question

My map function returns key-value pairs where key is the name of a field and the value is an object {type: <field type>, count : 1}.
For example suppose I have these documents:
{
"_id" : ObjectId("57611ad6bcc0d7e01be886c8"),
"index" : NumberInt(0)
}
{
"_id" : ObjectId("57611ad6bcc0d7e01be886c9"),
"index" : NumberInt(7)
}
{
"_id" : ObjectId("57611ad6bcc0d7e01be886c7"),
"index" : NumberInt(9)
}
I have to retrieve the name of each field, its type and the number of occurrences of the field in my collection.
My map function works and I get:
"_id", [{type:"ObjectId", count:1},{type:"ObjectId", count:1},{type:"ObjectId", count:1}]
"index",[{type:"number", count:1},{type:"number", count:1},{type:"number", count:1}]
I want to delete duplicates from type.
I have the following reduce function:
function (key, stuff) {
reduceVal = {type:"", count:0};
var array = [];
for(var idx =0; idx < stuff.length; idx++) {
reduceVal.count += stuff[idx].count;
if(array.indexOf(stuff[idx].type) > -1) {
array.push(stuff[idx].type);
}
}
reduceVal.type = array.toString();
The if clause does not work. My target is to add an element to my array just if it is not a duplicate.
Expected output:
"_id", {type:"ObjectId", count:3}
"index", {type:"number", count:3}
How can I fix?

Answer 1

The reduce function works. The if statement was wrong: I have to add an element to my array when
if(array.indexOf(stuff[idx].type) === -1).

Answer 2

It looks like you just jumbled up your reduce function. As far as I can interpret this, you assume that the reducer is called once globally. This is not the case. Instead, it is called per key, i.e. the input to the reducer is somthing like:
First call:
key = "ObjectId", val = [{type:"ObjectId", count:1},{type:"ObjectId", count:1},{type:"ObjectId", count:1}]
Second call:
key = "number", val = [{type:"number", count:1},...]
Therefore, you need to sum up, knowing that the key is already set (this code is not tested and will have its shortcomings):
function(key, vals) {
var sum = 0;
for(var i = 0; i < vals.length; i++) {
sum += vals[i].count;
}
return { "type" : key, "count" : sum };
}