[R] Summary Statistics for data.frame

[justin rapp]

I apologize for my constant questions but I am new to R and trying to
gain an appreciation for its capabilities.  The following task is easy
in Excel and I was hoping somebody could give me a quick explanation
for how it can be acheived in R so I can avoid having to switch
between the two applications.

How do I find the Summary Statistics in one Vector of the dataframe by
levels in another of the vectors.

For example, I have the following headings for my data.frame.
Conference
Year Drafted
Height
Weight
Ratio

I would like to see compute the mean Height, Weight, and Ratio as well
as their variances for each of the years under Year
Drafted(1980-2000).  What is the most efficient way of doing this?

Thank you.