Hello, 

I am trying to collect information of all samples but i don't know how to get all information for all samples.

I tired the following, is there a better way to do that ? 

gpl <- getGEO("GPL16791")
data <- gpl@header$sample_id

getInfo <- function(x){
      gps <- getGEO(x)
      gps <- unlist(gps@header)
      gps <- data.frame(gps, stringsAsFactors = F)
      gps <- t(gps)
      gps <- unique(gps)
      return(gps)
}
dat <- lapply(data, FUN = getInfo)

Check out the GEOmetadb package.  

library(GEOmetadb)
s = getSQLiteFile()
con = dbConnect(SQLite(),s)
res = dbGetQuery(con,"select gsm,title,gpl from gsm where gpl='GPL16791'")
dim(res)
head(res)