R 2.3.1, WinXP:
I have a puzzling problem that I suspect may be solved using
grep or a regular expression but am at a loss how to actually do it...
My data.frame looks like
Location Time X Y
-------- ---- --- ---
1 0 1.6 9.3
1 3 4.2 10.4
1 6 2.7 16.3
2 0 0.5 2.1
2 3 NA 3.6
2 3 5.0 0.06
2 6 3.4 14.0
and so forth. I would like to search for duplicate Time values
within a Location and take the numerical average (where possible)
of the elements in X and Y. These numerical averages should
then be used to create a single row where multiple rows once
existed. So, I would like to obtain
2 3 5.0 1.83
for the two Time = 3 rows for Location = 2 and use it to replace
these two rows. Ideally, avoiding for(i in 1:blah) loops would be
nice because the data.frame has about 10,000 rows that need to
be searched and processed. My intent is to do some comparing of
SAS to R -- the DATA step processing in SAS is quite fast and
using the RETAIN statement along with the LAG( ) function allows
this sort of thing to be done rapidly.
Thanks in advance,
Greg
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