Reducing an array of hashes into new hash - ruby

Question

I have an ActiveRecord relation that looks something like this:
[
{
timestamp: Tue, 02 Oct 2018 00:00:00 PDT -07:00,
user_id: 3,
organization_id: 1,
all_sales: 10,
direct_sales: 7,
referred_sales: 3,
},
{
timestamp: Wed, 03 Oct 2018 00:00:00 PDT -07:00,
user_id: 3,
organization_id: 1,
all_sales: 17,
direct_sales: 8,
referred_sales: 9,
},
{
timestamp: Thu, 04 Oct 2018 00:00:00 PDT -07:00,
user_id: 3,
all_sales: 3,
direct_sales: 3,
referred_sales: 0,
}
]
What I'd like to do is create a "sum" of all the keys pertaining to sales (for our purposes here, I don't need timestamp, user_id or organization_id, so basically, I'd like to end with something like this:
{
all_sales: 30
direct_sales: 18
referred_sales: 12
}
Is there an elegant ruby-ish way of doing this? I could easily create a set of variables for each sales category and augment them as I iterate over the original relation, but I wanted to see if the community had a cleaner method. In reality each of these hashes have far more than 3 relevant keys and so I fear that approach will get messy very quickly.
Edit: I also have checked out some other answers to similar questions here on SO (for example: Better way to sum values in an array of hashes), but ideally I wouldn't iterate so many times.

Answer 1

This will work:
arr.each_with_object({}) do |obj, hash|
%i[all_sales direct_sales referred_sales].each do |sym|
hash[sym] = hash[sym].to_i + obj[sym]
end
end
It's one iteration, you can write the nested loop as 3 different lines, but it's a bit cleaner this way in my opinion.
Note: calling to_i while getting previous value of hash[sym] as initially it is nil and nil.to_i == 0. Alternatively, you can initialize all unknown counts with 0, like this:
arr.each_with_object(Hash.new(0)) do |obj, hash|
%i[all_sales direct_sales referred_sales].each do |sym|
hash[sym] += obj[sym]
end
end

Answer 2

Since you're starting with an ActiveRecord Relation, you can use pluck to calculate all the sums with SQL and have it return an array with your totals:
SalesModel.pluck('SUM(all_sales)', 'SUM(direct_sales)', 'SUM(referred_sales)')
#=> [30, 18, 12]

Answer 3

Or use functional approach with reduce and merge methods:
keys = %i{all_sales direct_sales referred_sales}
total_sales = items.map {|item| item.select{|key, _| keys.include?(key)}}
.reduce({}) {|all, item| all.merge(item) {|_, sum, value| sum + value}}
# total_sales
# => {:all_sales=>30, :direct_sales=>18, :referred_sales=>12}
Or little bid clearer approach for Ruby 2.5.0 or higher, thanks to #Johan Wentholt
items.map {|item| item.slice(:all_sales, :direct_sales, :referred_sales)}
.reduce({}) {|all, item| all.merge(item) {|_, sum, value| sum + value}}
# => {:all_sales=>30, :direct_sales=>18, :referred_sales=>12}

Answer 4

Use Merge and Reduce function
value = arr.reduce do |h1, h2|
h1.merge(h2) do |k, v1, v2|
[:all_sales, :direct_sales, :referred_sales].include?(k) ? (v1 + v2) : nil
end
end.reject {|_, v| v.nil?}
p value

Answer 5

A couple of more verbose other options (that can be rendered more DRY and general):
result = { all_sales: (array.sum{ |e| e[:all_sales] }), direct_sales: (array.sum{ |e| e[:direct_sales] }), referred_sales: (array.sum{ |e| e[:referred_sales] }) }
or:
result = array.each.with_object(Hash.new(0)) do |h, obj|
obj[:all_sales] += h[:all_sales]
obj[:direct_sales] += h[:direct_sales]
obj[:referred_sales] += h[:referred_sales]
end
To be more DRY and general, starting with the array of the required keys
keys = [:all_sales, :direct_sales, :referred_sales]
The first becomes
keys.map.with_object(Hash.new) { |k, obj| obj[k] = array.sum { |e| e[k] } }
and the second:
array.each.with_object(Hash.new(0)) { |h, obj| keys.each { |k| obj[k] += h[k] } }