Hi all,
I have a table (t) of the following format (first row is the header):
A       x1        x2
c       1          NA
c       2          1002
c       3           NA
a       4          1004
b       5           NA
c        6          1006
c        7          1007
c        8          1008
b        9          1009
a       10         1010
a       11         1011
c       12         1012
c       13         1013
a       14         1014
c        NA        1015


I want to find the mean of all the values corresponding to the row names
"a", "b", "c" (which are duplicated).
I tried the following which works:
U <- unique(t$A)
tt <- t(sapply(U, FUN=function(u) {mean(na.omit(t[t$A==u, ]))}))

However, in reality the table t is real huge ( almost 44K rows and 100
columns). The above approach takes too long. Is there another alternative
that anyone can think of.

Thanks a lot for any help/suggestions.

Sincerely,
Hari

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