R/sample.R

In edwindj/ffbase2: Dplyr for 'ff'

#' @export
sample_n.ffdf <- function(tbl, size, replace=FALSE, weight=NULL
                          , .env=parent.frame()){
  open(tbl)
  on.exit(close(tbl))

  if (!missing(weight)) {
    weight <- eval(substitute(weight), tbl, .env)
  }
  
  sample_n_basic(tbl, size, replace=replace, weight=weight)
}

#' @export
sample_frac.ffdf <- function(tbl, size=1, replace=FALSE, weight=NULL
                             , .env=parent.frame()){
  if (!missing(weight)) {
    weight <- eval(substitute(weight), tbl, .env)
  }
  sample_n.ffdf(tbl, round(size*nrow(tbl)), replace=replace, weight=weight)
}

sample_n_basic <-
  function (tbl, size, replace = FALSE, weight = NULL) 
  {
    n <- nrow(tbl)
    weight <- check_weight(weight, n)
    assert_that(is.numeric(size), length(size) == 1, size >= 
                  0)
    check_size(size, n, replace)
    idx <- sample.int(n, size, replace = replace, prob = weight)
    tbl[as.ff(idx), , drop = FALSE]
  }