r - Getting the mean value for every Id in a data frame -

Imagine I have a data frame with 2 columns

  ID value of 12 13 32 3 6022 11 9 142 231 12 23 119 312 ...  

And I want to get the mean value for each "id". Do you know any fast way to do this?

Overall, other options include DDPA (in Plyr)