Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/9031#discussion_r41699843
--- Diff: R/pkg/R/DataFrame.R ---
@@ -1881,3 +1881,33 @@ setMethod("as.data.frame",
}
collect(x)
})
+
+#' The specified DataFrame is attached to the R search path. This means
that
+#' the DataFrame is searched by R when evaluating a variable, so columns in
+#' the DataFrame can be accessed by simply giving their names.
+#'
+#' @rdname attach
+#' @title Attach DataFrame to R search path
+#' @param what (DataFrame) The DataFrame to attach
+#' @param pos (integer) Specify position in search() where to attach.
+#' @param name (character) Name to use for the attached DataFrame. Names
+#' starting with package: are reserved for library.
+#' @param warn.conflicts (logical) If TRUE, warnings are printed about
conflicts
+#' from attaching the database, unless that DataFrame contains an object
+#' @examples
+#' \dontrun{
+#' attach(irisDf)
+#' summary(Sepal_Width)
+#' }
+#' @seealso \link{detach}
+setMethod("attach",
+ signature(what = "DataFrame"),
+ function(what, pos = 2, name = deparse(substitute(what)),
warn.conflicts = TRUE) {
+ bf <- what
+ cols <- columns(bf)
+ newEnv <- new.env()
+ for (i in 1:length(cols)) {
--- End diff --
I'm not sure we can do that now from R:
```
> a <- list()
> b <- createDataFrame(sqlContext, a)
Error in take(x, 1)[[1]] : subscript out of bounds
> a <- data.frame()
> a
data frame with 0 columns and 0 rows
> b <- createDataFrame(sqlContext, a)
Error in FUN(X[[i]], ...) : can not infer type from NULL
```
Or 0-col DataFrame being very useful?
Though I agree we could check for it, in case that support is added in the
future. I'd suggest either adding a `stopifnot()` or a test case for that?
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