blocksample(data, size, idvar = NULL, replace = TRUE, ...)

d <- data.frame(x=rnorm(5), z=rnorm(5), id=c(4,10,10,5,5), v=rnorm(5))
(dd <- blocksample(d,size=20,~id))
attributes(dd)$id

## Not run: 
blocksample(data.table::data.table(d),1e6,~id)

## End(Not run)


d <- data.frame(x=c(1,rnorm(9)),
               z=rnorm(10),
               id=c(4,10,10,5,5,4,4,5,10,5),
               id2=c(1,1,2,1,2,1,1,1,1,2),
               v=rnorm(10))
dsample(d,~id, size=2)
dsample(d,.~id+id2)
dsample(d,x+z~id|x>0,size=5)