[ENH] Group-by widget.

[ajdapretnar]

Feature Request

Have the option in Geo Map to have the size of the dot correspond to the sum of instances with the same lat/lon value.

E.g.

lat	lon
46.3	14.3
46.3	14.3
46.3	14.3
45.1	13.2
45.1	13.2

The first three instances would be plotted as one large dot, the last two as a smaller dot.

[kernc]

This is a group-by–count operation which doesn't belong into this widget in my opinion. Any vis widget could benefit from additional aggregate data that group-by provides, such as occurrence counts.

We shouldn't intend to maintain the same code in two places. FWIU, Geo Map in core is deprecated in favor of the Geo add-on.

[janezd]

This will be fixed in #2860, the famous pivot widget.