Ember.js: Summarize model records into one record - ember.js

Question

I thought I had this figured out using reduce(), but the twist is that I need to roll up multiple properties on each record, so every time I am returning an object, and the problem I'm having is that previousValue is an Ember Object, and I'm returning a plain object, so it works fine on the first loop, but the second time through, a is no longer an Ember object, so I get an error saying a.get is not a function. Sample code:
/*
filter the model to get only one food category, which is determined by the user selecting a choice that sets the property: theCategory
*/
var foodByCategory = get(this, 'model').filter(function(rec) {
return get(rec, 'category') === theCategory;
});
/*
Now, roll up all the food records to get a total
of all cost, salePrice, and weight
*/
summary = foodByCategory.reduce(function(a,b){
return {
cost: a.get('cost') + b.get('cost'),
salePrice: a.get('salePrice') + b.get('salePrice'),
weight: a.get('weight') + b.get('weight')
};
});
Am I going about this all wrong? Is there a better way to roll up multiple records from the model into one record, or do I just need to either flatten out the model records into plain objects first, or alternatively, return an Ember object in the reduce()?
Edit: doing return Ember.Object.create({...}) does work, but I still would like some opinion on whether this is the best way to achieve the goal, or if Ember provides functions that will do this, and if so, if they're any better than reduce.

Answer 1

Assuming this.get('model') returns an Ember.Enumerable, you can use filterBy instead of filter:
var foodByCategory = get(this, 'model').filterBy('category', theCategory);
As for your reduce, I don't know of any Ember built-ins that would improve it. The best I can think of is using multiple, separate mapBy and reduce calls:
summary = {
cost: foodByCategory.mapBy('cost').reduce(...),
salePrice: foodByCategory.mapBy('salePrice').reduce(...),
...
};
But that's probably less performant. I wouldn't worry too much about using Ember built-ins to do standard data manipulation... most Ember projects I know of still use a utility library (like Lodash) alongside Ember itself, which usually ends being more effective when writing this sort of data transformation.