Ruby on Rails iterate through column efficiently - sql

Question

created_at iteration group_hits_per_iteration
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2019-11-08 08:14:05.170492 300 34
2019-11-08 08:14:05.183277 300 24
2019-11-08 08:14:05.196785 300 63
2019-11-08 08:14:05.333424 300 22
2019-11-08 08:14:05.549140 300 1
2019-11-08 08:14:05.576509 300 15
2019-11-08 08:44:05.832730 301 69
2019-11-08 08:44:05.850111 301 56
2019-11-08 08:44:05.866771 301 18
2019-11-08 08:44:06.310749 301 14
Hello
My goal is to create a sum total of the values in 'group_hits_per_iteration' for each unique value in the 'iteration column' which will then be graphed using chartkick.
For example, for iteration 300 I would sum together 34,24,63,22,1,15 for a total of 159, then repeat for each unique entry.
The code I've included below does work and generates the required output but it's slow and gets slower the more data is read into the database.
It creates a hash that is fed into chartkick.
hsh = {}
Group.pluck(:iteration).uniq.each do |x|
date = Group.where("iteration = #{x}").pluck(:created_at).first.localtime
itsum = Group.where("iteration = #{x}").pluck('SUM(group_hits_per_iteration)' )
hsh[date] = itsum
end
<%= line_chart [
{name: "#{#groupdata1.first.networkid}", data: hsh}
] %>
I'm looking for other ways to approach this, I was thinking of having SQL do the heavy lifting and not do the calculations in rails but not really sure how to approach that.
Thanks for the help.

Answer 1

If you want to get just the sums for every iteration, following code should work:
# new lines only for readability
group_totals =
Group
.select('iteration, min(created_at) AS created_at, sum(group_hits_per_iteration) AS hits')
.group('iteration')
.order('iteration') # I suppose you want the results in some order
group_totals.each do |group|
group.iteration # => 300
group.hits # => 159
group.created_at # => 2019-11-08 08:14:05.170492
end
In this case all the hard work is done by the database, you can just read the results in your ruby code.
Note: In your code you are taking first created_at for every iteration, I took the lowest date