Counting and grouping at the same time

Question

I have a Mail model with the following schema:

t.string   \"mail\"
t.integer  \"country\"
t.boolean  \"validated\"
t.datetime \"created_at\"
t.d         


        

Answer 1

With Rails 3 you can simplify it further:

Mail.where(validated: true).count(group: :country)

You can order by fields in the group - in this case only :country would be valid:

Mail.where(validated: true)
    .order(:country)
    .count(group: :country)

You can also order by the count, using "count_all":

Mail.where(validated: true)
    .order("count_all desc")
    .count(group: :country)

You can also limit the number of groups returned. To do this you must call limit before calling count (because #count returns ActiveSupport::OrderedHash):

Mail.where(validated: true)
    .order("count_all desc")
    .limit(5)
    .count(group: :country)

Updated syntax for Rails 4:

Mail.where(validated: true)
    .group(:country)
    .count

Answer 2

Mail.find(
    :all, 
    :select => 'count(*) count, country', 
    :group => 'country', 
    :conditions => ['validated = ?', 't' ], 
    :order => 'count DESC',
    :limit => 5)

This should give you records that have a country attribute and a count attribute.

Answer 3

Try:

Mail.count(:group => 'country', :conditions => ['validated = ?', 't'])

I'm not sure count accepts :limit though.

EDIT:

I think this is more readable:

Mail.count(:group => :country, :conditions => {:validated => true})

Answer 4

I too had to group data with city name and showing count of how many rows are there for each city with specific condition. So this is how I did:

CityData.where(:status => 1).group(:city_name).count

Output of this was:

{:Mumbai => 10, :Dublin => 7, :SF => 9}