R matrix: unique by one column, add the values on other column and concatenate the values on other -

in r have matrix

>      id    size pattern                                  [1,] "1"   "24"  "100" [2,] "2"   "10"  "111" [3,] "3"   "2"   "111" 

and want unique pattern, add size , concatenate id:

 >       id   size pattern                                   [1,] "1"    "24"  "100"  [2,] "2-3"  "12"  "111" (this pattern duplicated, add size , concatenate id)  

i can do:

> = unique(a[,"pattern"]) 

but couldn't figure out how add , concatenate.

thanks in advance!

if have columns want treat numeric (adding values together) , want treat character (pasting them) matrix isn't right structure data. should using data frame.

using plyr:

library(plyr) ddply(data.frame(a), .(pattern), summarise,        id=paste(id, collapse="-"),       size=sum(as.numeric(size)))