How do I group by day instead of date?

问题:

ok so i have

 >> list = Request.find_all_by_artist("someBand")
=> [#<Request id: 1, artist: "someBand", song: "someSong", venue: "Knebworth - Stevenage, United Kingdom", showdate: "2011-07-01", amount: nil, user_id: 2, created_at: "2011-01-01 18:14:08", updated_at: "2011-01-01 18:14:09".............

and then

list.group_by(&:created_at).map {|k,v| [k, v.length]}.sort
=> [[Sat, 01 Jan 2011 18:14:08 UTC +00:00, 10], [Sun, 09 Jan 2011 18:34:19 UTC +00:00, 1], [Sun, 09 Jan 2011 18:38:48 UTC +00:00, 1], [Sun, 09 Jan 2011 18:51:10 UTC +00:00, 1], [Sun, 09 Jan 2011 18:52:30 UTC +00:00, 1], [Thu, 10 Feb 2011 02:22:08 UTC +00:00, 1], [Thu, 10 Feb 2011 20:02:20 UTC +00:00, 1]]

the problem is I have a few Sun, 09 Jan and a couple for the 10th, instead of one like this

this is what i need

=> [[Sat, 01 Jan 2011 18:14:08 UTC +00:00, 10], [Sun, 09 Jan 2011 18:34:19 UTC +00:00, 4], [Thu, 10 Feb 2011 20:02:20 UTC +00:00, 2]]

回答1:

Time is a quite complex object to group by. Assuming you want to group by the creation date, instead of the full Time, start creating a custom method in your model to return the group criteria.

The method should return the creation date, possibly as string.

def group_by_criteria
  created_at.to_date.to_s(:db)
end

Then, group by that method.

list.group_by(&:group_by_criteria).map {|k,v| [k, v.length]}.sort

回答2:

I think this is a much more elegant and simple solution

list.group_by{|x| x.created_at.strftime("%Y-%m-%d")} 

回答3:

There is a gem for that: groupdate.

Usage (from the docs):

User.group_by_day(:created_at).count
# {
#   2013-04-16 00:00:00 UTC => 50,
#   2013-04-17 00:00:00 UTC => 100,
#   2013-04-18 00:00:00 UTC => 34
# }

回答4:

Ipsum's answer is actually good and probably the best:

In Arel:

requests = Arel::Table.new(:requests)
query = requests.project("COUNT(*), CAST(requests.created_at AS DATE) as created_at")
query = query.group("CAST (requests.created_at AS DATE)")
Request.find_by_sql(query.to_sql)

回答5:

Group without extra gems:

def self.group_by_day items
   data = items.group_by{|x| x.created_at.to_date}
   chart_data = {}

   data.each do |a,b|
     chart_data.merge!({a => b.count})
   end

   return chart_data
end

回答6:

you can use GROUP BY DATE(created_at) in MySQL

On ruby code you can use like this

list.group('DATE(created_at)').map {|k,v| [k, v.length]}.sort