[R] Adding same items together in data.frame

From: wong, honkit (Stephen) <honkit_at_stanford.edu>
Date: Fri, 13 May 2011 16:06:10 -0700

Dear All,
I am new to R. I have a 2 column data frame with more than ten thousand rows. Something like below. I want to add up all duplicated items, e.g. the three "aa" add up together to get a single value gene=a, value=74. How can I do that?? Thanks for help !
gene value

aa	 20
bb 	10
cc	 9
aa 	30
aa 	24
dd	 100
ee 	55

.... ...
Millions thanks.
Best Regards,

WONG, Hon-Kit (Stephen)
Cleary Lab, Dept of Pathology
Stanford University

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