Generate array of daily avg values from db table (Rails) - ruby-on-rails

Question

Context:
Trying to generating an array with 1 element for each created_at day in db table. Each element is the average of the points (integer) column from records with that created_at day.
This will later be graphed to display the avg number of points on each day.
Result:
I've been successful in doing this, but it feels like an unnecessary amount of code to generate the desired result.
Code:
def daily_avg
# get all data for current user
records = current_user.rounds
# make array of long dates
long_date_array = records.pluck(:created_at)
# create array to store short dates
short_date_array = []
# remove time of day
long_date_array.each do |date|
short_date_array << date.strftime('%Y%m%d')
end
# remove duplicate dates
short_date_array.uniq!
# array of avg by date
array_of_avg_values = []
# iterate through each day
short_date_array.each do |date|
temp_array = []
# make array of records with this day
records.each do |record|
if date === record.created_at.strftime('%Y%m%d')
temp_array << record.audio_points
end
end
# calc avg by day and append to array_of_avg_values
array_of_avg_values << temp_array.inject(0.0) { |sum, el| sum + el } / temp_array.size
end
render json: array_of_avg_values
end
Question:
I think this is a common extraction problem needing to be solved by lots of applications, so I'm wondering if there's a known repeatable pattern for solving something like this?
Or a more optimal way to solve this?
(I'm barely a junior developer so any advice you can share would be appreciated!)

Answer 1

Yes, that's a lot of unnecessary stuff when you can just go down to SQL to do it (I'm assuming you have a class called Round in your app):
class Round
DAILY_AVERAGE_SELECT = "SELECT
DATE(rounds.created_at) AS day_date,
AVG(rounds.audio_points) AS audio_points
FROM rounds
WHERE rounds.user_id = ?
GROUP BY DATE(rounds.created_at)
"
def self.daily_average(user_id)
connection.select_all(sanitize_sql_array([DAILY_AVERAGE_SELECT, user_id]), "daily-average")
end
end
Doing this straight into the database will be faster (and also include less code) than doing it in ruby as you're doing now.

Answer 2

I advice you to do something like this:
grouped =
records.order(:created_at).group_by do |r|
r.created_at.strftime('%Y%m%d')
end
At first here you generate proper SQL near to that you wish to get in first approximation, then group result records by created_at field converted to just a date.
points =
grouped.map do |(date, values)|
[ date, values.reduce(0.0, :audio_points) / values.size ]
end.to_h
# => { "1-1-1970" => 155.0, ... }
Then you remap your grouped hash via array, to calculate average values with audio_points.

Answer 3

You can use group and calculations methods built in AR: http://guides.rubyonrails.org/active_record_querying.html#group
http://guides.rubyonrails.org/active_record_querying.html#calculations