[R] Adding same items together in data.frame

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

Re: [R] Adding same items together in data.frame

Stem Cell Research Building, Room G2035 259 Campus Drive Stanford, CA 94305 -Original Message- From: Dennis Murphy [mailto:djmu...@gmail.com] Sent: Friday, May 13, 2011 8:05 PM To: wong, honkit (Stephen) Cc: r-help@r-project.org Subject: Re: [R] Adding same items together in data.frame