I have a rails app with a PostgreSQL database with hourly price data for the last 10 years, and I need to get the daily average price for each day saved in a new DB table. This query groups records by day and returns an average price for each day:
averages = Sale.average(:price, :group => "DATE_TRUNC('day', date)")
The Rails Console response looks like this (a sample of 2 days of data):
{"2013-01-03 00:00:00"=>#<BigDecimal:7fcc7c2e4a28,'0.1752888888 88888889E2',27(27)>, "2013-01-02 00:00:00"=>#<BigDecimal:7fcc7c2e4848,'0.2547086956 52173913E2',27(27)>}
Can anyone suggest how to write some code to save these returned date and averageprice values to a new Object called DailyAverage?
Your response is like:
{
'date' => BigDecimal,
'date2' => BigDecimal,
'date2' => BigDecimal,
}
So you can access to each average for each date like this:
averages = Sale.average(:price, :group => "DATE_TRUNC('day', date)")
averages.each do |date, avg|
DailyAverage.create(date: date, average: avg.to_f)
end
This code assumes you have a DailyAverage model with date and average attributes.
You may have to use a to_date in the each loop:
averages.each do |date, avg|
DailyAverage.create(date: date.to_date, average: avg.to_f)
end
Related
I have a series of Appointments where the date and time is stored under start_date as DateTime. I'd like to categorize them as starting in the Morning, Daytime, or Evening. I created an array of hashes with labels and ranges I used for a SQL statement where I convert the start_date records into seconds using CAST(EXTRACT (EPOCH FROM start_time) AS INT)
TIME_RANGES = [
{label: "Morning", min: 0, max: 32399},
{label: "Daytime", min: 32400, max: 61199},
{label: "Evening", min: 61200, max: 86399}
]
cases = TIME_RANGES.map do |r|
"when CAST (EXTRACT (EPOCH FROM start_date) AS INT) % 86400 between '#{r[:min]}' and '#{r[:max]}' then '#{r[:label]}'"
end
time_ranges = Appointment.select("count(*) as n, case #{time_cases.join(' ')} end as time_range").group('time_range')
This takes the number of seconds in a day (86400) and labels the appointments based on the modulo of the start_date with 86400. However, a number of appointments take place in different timezones, but they're all stored as UTC. So an appointment at 08:00 AM EST is equivalent to one at 07:00 AM CST, but both are stored internally as 12:00 PM UTC. This would cause the appointments to be incorrectly labelled as "Daytime" when they're intended to be "Morning" (from the perspective of the User booking it).
Ideally, I would like some way to convert the start_date based on the User's timezone to make it look like it occurred in UTC. So I would want a 12:00 PM EST appointment to be labelled as if it were a 12:00 PM UTC appointment instead of 04:00 PM UTC. More specifically, I would like to subtract 14400 seconds from the converted start_date before performing the modulo.
I can join Appoinments to Users, which contains the User's timezone. How can I incorporate this information into my query above, so that a modified start_date is used for each record, depending on the User's timezone in that same record?
I know I could accomplish this with a loop of each timezone and adding/substracting a specific amount of seconds in each loop, then combining the results of all the loops, but I was wondering if there was a way to do it in one query.
Per my comment, I am assuming we have three tables: appointments, users, and preferences. In appointments we have start_date and user_id. In users we have preference_id. In preferences we have some column that names the time zone, so I'll call that tz_name.
Note: Postgres timezone functions are messy. I would highly recommend you read up on them. This excellent article is a good place to start.
It is possible to use pure SQL to generate the time ranges and return a grouped result. A pure SQL solution would be best if you need to label and group many records (thousands or more) at a time.
Assuming you are working with 1000 records or fewer at a time, you'll probably want to use Rails scopes, as this will give you an ActiveRecord result. Then you'll do your grouping using Ruby's Array methods.
That solution would look something like this:
# app/user.rb
class User < ApplicationRecord
belongs_to :preference
has_many :appointments
end
# app/appointment.rb
class Appointment < ApplicationRecord
belongs_to :user
scope :with_seconds, lambda {
joins(user: :preference)
.select('appointments.*, extract(epoch from timezone(tz_name, start_date::timestamptz)::time)::int as seconds')
}
# This method is optional. If it is excluded, calling #seconds
# on an appointment instance will raise an error if the
# .with_seconds scope has not been applied.
def seconds
attributes['seconds']
end
def time_range
return nil unless seconds.present?
if seconds.between?(0, 32_399)
'Morning'
elsif seconds.between?(32_400, 61_199)
'Daytime'
else
'Evening'
end
end
end
The select portion of the scope probably deserves some explanation.
start_date::timestamptz: Take the start_date, which is stored as a Postgres timestamp, and convert it into a Postgres timestamp with time zone in the time zone of the Postgres server (presumably UTC).
timezone(tz_name, start_date::timestamptz): Convert the timestamp with time zone back into a timestamp type in the local time of the tz_name time zone.
timezone(tz_name, start_date::timestamptz)::time: Drop the date and keep the time component.
Then we extract epoch from that time component, which converts it into seconds.
Finally we convert the result to an integer to avoid anything falling through the cracks when we determine the time range.
Now you can do:
Appointment.all.with_seconds.group_by(&:time_range)
or
user = User.first
user.appointments.with_seconds.group_by(&:time_range)
For a pure SQL solution that will return ids grouped under the three time ranges, add this method to your Appointment model:
def self.grouped_by_time_range
current_scope = with_seconds.to_sql
query = <<~SQL
with converted_seconds as (#{current_scope})
select array_agg(id) as ids, case when seconds < 32400 then 'Morning'
when seconds < 61200 then 'Daytime'
else 'Evening' end as time_range
from converted_seconds
group by time_range
SQL
result = ActiveRecord::Base.connection.execute(query.squish)
result.to_a
end
If you don't need strictly SQL based solution you might use Ruby's select method to extract this appointments as in this example:
(I am assuming there is some kind of tz_name field in appointment model which holds timezone name)
morning_appointments = Appointment.all.select do |a|
a.start_date.in_time_zone(a.tz_name).hour > 6 && a.start_date.in_time_zone(a.tz_name).hour < 20
end
Edit:
Thanks #moveson for pointing out my mistake, I changed solution a bit.
I have Payment model with data and amount attributes. Now I need to get all the records for the current week on the page. I want to use some kind of pagination, e.g.: On the first page I get all records for the current week, on the second page - records from the previous week etc.
And on every page I need to get total amount for this week and average amount per day.
So, I have two questions:
How to get all the records for particular week on the page?
How to count amount for this week?
Now everything I've done was array with weeks and amounts
def self.count_by_week
raw_result = group_by_week_and_state.count
# {['2014-12-01-2014-12-07', 'foo'] => 100, ['2014-12-01-2014-12-07', 'bar'] => 100, '...' => '...'}
raw_result.each_with_object({}) do |(k, v), result|
result[k[0]] ||= {}
result[k[0]][k[1]] = v
end
end
def self.group_by_week_and_state
group("#{weekday_query(0)} || \'-\' || #{weekday_query(6)}").group('amount')
end
# build sql part for day offset of week (0 => mon, 6 => sun)
def self.weekday_query(offset)
"to_char(cast(date_trunc(\'week\', created_at) as date) + #{offset}, \'YYYY-MM-DD\')"
end
You could use the groupdate gem to accomplish this.
https://github.com/ankane/groupdate
Once you have successfully grouped your records, it's just too simple to get the sum for each groups.
Im trying to gather all sales made within a week and put each sale in day made. If Moday was two sales, then Monday => {...}, {...} etc
"Monday" would be ruby's date format.
In my db I have 5 sale objects: Two sales on Monday and two on Tuesday.
Controller:
def daily_customer_sale(created)
date_and_id = Sale.where('created_at >= ?', created).pluck(:created_at, :id)
date_and_id.each do |obj|
yield(obj.first, obj.last)
end
end
def daily_sales(created=nil)
sales_by_date = Hash.new(0)
daily_customer_sale(created) do |date, id|
s_date = date.to_date
sales_by_date[s_date] = Sale.find(id) # Seems to return only one object per day
end
return sales_by_date
end
For views:
daily_sales(1.week.ago.to_datetime)
What I get in two dates (correct) in which each data has only one object when it should be two or more per date. Is there something wrong?
You don't need complex logic to do it. Here is a cleaner way
Sale.where('created_at >= ?', created_at).group_by{ |sale| sale.created_at.to_date}
It will return All the sales grouped by day.
key will be date object and for each day there will be sale array containing all of the sales for that day.
If you need string based key you can format it as you like as per below
Sale.where('created_at >= ?', created_at).group_by{ |sale| sale.created_at.to_date.to_s } #default date format
Sale.where('created_at >= ?', created_at).group_by{ |sale| sale.created_at.to_date.strftime("%d/%m/%Y") } #23/09/2016
You can have a look at Group by method
I have a model (Expense) that contains fields like 'cost'.
I'd like to iterate through all my expenses to find the sum of the cost for all entries belonging to a particular month.
Is there a way to do it in rails directly?
Expense.find(:all, :conditions => .....)
To get the SUM of costs for the month of a given date:
# date = any day of the month of intrest
Expense.sum(:cost, :conditions => {:created_at =>
(date.beginning_of_month..date.end_of_month)})
To get the sum of costs of all the months:
Expense.sum(:cost,
:group => "EXTRACT(YEAR_MONTH FROM created_at)").each do |y_m, cost_sum|
p "#{y_m}-#{cost_sum}"
end
In the above call, use the conditions option to restrict the result-set to a date range.
sum/group_by:
Expense.find(:all,
:select => "SUM(cost) as cost_sum, MONTH(date) as month, YEAR(date) as year",
:group => "MONTH(date), YEAR(date)" )
Have a look at this beautiful gem: https://github.com/radar/by_star
I have a table with a float called 'cost' and timestamp called'created_at'.
I would like it to output an array with the summing the costs for each particular day in the last month.
Something like:
#newarray = [] #creating the new array
month = Date.today.month # Current Month
year = Date.today.year # Current Year
counter = 1 # First Day of month
31.times do #for each day of the month (max 31)
#adding sales figures for that day
#newarray.push(Order.sum(:cost, :conditions => {:created_at => "#{year}-#{month}-#{counter}"}))
counter = counter + 1 #go onto next day
end
However this doesn't work as all the timestamps have a time as well.
Apologies in advance for the poor title, I can't seem to think of a sensible one.
You should be able to use code like the following:
sales_by_day = Order.sum(:cost,
:group => 'DATE(created_at)',
:conditions => ['DATE(created_at) > ?', 31.days.ago])
(0..30).collect { |d| sales_by_day[d.days.ago.to_date.to_s] || 0 }.reverse
This will sum the order cost by day, then create an array with index 0 being the last 24 hours. It will also take only one query, whereas your example would take 31.
To change the cut off date, replace 31.days.ago with an instance of the Time class. Documentation here: http://ruby-doc.org/core/classes/Time.html
Good luck!
This should work:
(Date.today.beginning_of_month..Date.today.end_of_month).map { |d|
Order.sum(:cost, :conditions => ['created_at >= ? AND created_at < ?', d, d+1])
}
Although I think you should try getting it using a single query, instead of making one for each day.