R help - Mar 2014 - Bootstrapping mean for two and more variables by group

Hi R User, 
Would you give me some hints on how I can calculate bootstrapping mean+-SE for
each column  based by group. I searched it but I could not get what I wanted.
For example I have these data set
data <- as.data.table(list(x1 = runif(200), x2 = runif(200), group =
runif(200)>0.5))
I wanted to have the table with real mean and bootstrapping mean (999times) +-SE
for each group (TRUE and FALSE) in each column (x1 and x2). It should be simple
but I could not.....
would you give me some hints? I will really appreciate for your help. 
Thanks 
KG

 		 	   		  
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