how to "group" data ?

Hi,

Let's say that in Graphite, I have this kind of informations :

stats.timers.servers.SERVER_1.orders.SHOP_1.count
stats.timers.servers.SERVER_1.orders.SHOP_2.count
stats.timers.servers.SERVER_2.orders.SHOP_1.count
stats.timers.servers.SERVER_2.orders.SHOP_2.count

Then, I would like to monitor the total number of orders.
For doing this, I graphed this target "stats.timers.servers.*.orders.*.count" and set "areaMode=stacked"

Each column of the resulting histogramm represents : "sum(orders by server by shop)"

How, can I change this so that it's actually grouped by server ? I want to have "sum(orders by shop)"

I tried with "group(stats.timers.servers.\*.orders.*.count)", but the result looks weird :-S
I can't find any documentation about the "group()" function ...

cheers
Nicolas