building mean/median over subgroups

Dear all,

I'm trying to solve the following problem, and hoping to get some advise 
here from the group

I have a dataframe in which the same sample was measured more than once 
on the same day. I would reorganize the dataframe to get a single value 
(mean /median) for one day

Patient    Day    Sample    Test
A    1    A    23
A    1    A    36
A    5    B    44
A    5    B    23
B    2    C    10
B    2    C    5


mean

Patient    Day    Sample    Test.mean
A    1    A    29.5
A    5    A    33.5
B    2    C    7.5


it would be great to get some help form the list.

Yours
Frank

Dear all,

I'm trying to solve the following problem, and hoping to get some 
advise here from the group

I have a dataframe in which the same sample was measured more than 
once on the same day. I would reorganize the dataframe to get a 
single value (mean /median) for one day

Patient	Day	Sample	Test
A	1	A	23
A	1	A	36
A	5	B	44
A	5	B	23
B	2	C	10
B	2	C	5


mean

Patient	Day	Sample	Test.mean
A	1	A	29.5
A	5	A	33.5
B	2	C	7.5


it would be great to get some help form the list.

Yours
Frank
-- 
Frank Mattes, MD			e-mail:	f.mattes at ucl.ac.uk