Try the function groupMeans() from the S+Resample library.
Download info below.
That computes all group means; you could then subscript to get only
the rows that had repeated values of ID; e.g.
groupMeans(x)[ unique(x$ID[duplicated(x$ID)]), ]
>I have data frame as follows:
>
>ID ratio_1 ratio_2
>X 2.5 2.0
>Y 3.6 2.1
>Y 2.9 1.2
>Y 3.5 4.2
>Z 2.5 1.9
>K 0.5 2.1
>L 1.4 4.1
>
>I would like average values of columns ratio_1, ratio_2 for all the IDs with
>multiple values, i.e. ID Y would have average ratio_1 = 3.3333, ratio_2.5.
>I am a novice S_PLUS user, sorry for the trivial question. Thanks.
>
>Sohail Khan
>Scientific Programmer
>COLD SPRING HARBOR LABORATORY
>Genome Research Center
>500 Sunnyside Boulevard
>Woodbury, NY 11797
>(516)422-4076
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