Line Chart Y axis issue

I have an xml data source which represents a sets of events completed.
I need to build a line chart where X axis represents events timeline and Y axis the total number of events completed by given date
My issue is that I do not have the Y axis data and I'd need to build this info dynamically.

e.g (data source)

Event ID | Finish Date
1 03-Jan-2013
2 05-Jan-2013
3 20-Jan-2013
4 21-Jan-2013
5 02-Feb-2013
6 11-Feb-2013
7 22-Feb-2013
8 01-Mar-2013
9 03-Mar-2013
10 05-Mar-2013

The required line chart graph should be similar to ( on Y axis I need to have total number of events completed for each finish date reported) the following graph

Any help on how I could retrieve count of completed events dynamically ? Maybe using scripting?
Thanks in advance for any help or example.