Rails - How to create advanced arrays that sums columns?

How do I create an array that sums the column earn on a date.

So it would output like:

[<sum of 'earn' where dato=2011-02-14>, <sum of 'earn' where dato=2011-02-15>]

And how to create a pointstart, that finds the last date.

My table

id  virksomhed  dato                   earn     
9   Euroads     2011-02-15 00:00:00     4 
10  Euroads     2011-02-15 00:00:00     4   
11  Iqmedier    2011-02-15 00:00:00     2   
12  Iqmedier    2011-02-15 00:00:00     3   
12  Iqmedier    2011-02-14 00:00:00     3  

{
        name: "Indtjening",
        pointInterval: <%= 1.day * 1000 %>,
        pointStart: How to create point start,
        data: 
      },
       {
        name: "Iqmedier",
        color: '#DBD200',
        pointInterval: <%= 1.day * 1000 %>开发者_如何学JAVA,
        pointStart: How to create point start,
        data: <%= Reklamer.where(:virksomhed => 'Iqmedier').all.map(&:earn) %>
      }
      ,
       {
        name: "Euroads",
        color: '#1B7B94',
        pointInterval: <%= 1.day.to_i * 1000 %>,
        pointStart: How to create point start,
        data: <%= Reklamer.where(:virksomhed => 'Euroads').all.map(&:earn) %>
      }

Reklamer.sum(:earn, :group => :dato)
#<OrderedHash { 2011-02-14 00:00:00 => 3, 2011-02-15 00:00:00 => 13}>

Model.find(:all, :select => 'sum(earn) AS earn', :group => 'dato').map(&:earn)