[R] Calculates the mean/median from grouped data in R?

[David Winsemius]

On May 7, 2013, at 8:40 PM, jpm miao wrote:

> Is there a function in R that calculate the mean and median for a grouped
> data?
> For example, a survey shows the oil price outlook in the future. How can I
> calculate the mean/median?
> (Of course, I understand that the groups "below 80" and "above 110" must be
> defined more specifically)
> 
>  below 80 4  80-90 5  90-100 8  100-110 7  above 110 3
> 

Why would all groups need to be defined more specifically? How do we know whether items in the 80-90 range are evenly distributed? .... could be 80, 81, 82, 84, 85 or all 89's.

David Winsemius
Alameda, CA, USA