Adaptative mean on data

Hi to all, I have two columns, one with date and one with values. For each dates I have more values, like this:

22/06/2006 -1

22/06/2006 -2

22/06/2006 -1

...

but not same number of values for each days (ex: 22/06/2006 3 values, 23/06/2006 12 values ecc...).

I need a mean of these values for each day. Is it possible ?

Thanks in advance