[SPARK-20550][SPARKR] R wrapper for Dataset.alias

## What changes were proposed in this pull request?

- Add SparkR wrapper for `Dataset.alias`.
- Adjust roxygen annotations for `functions.alias` (including example usage).

## How was this patch tested?

Unit tests, `check_cran.sh`.

Author: zero323 <zero323@users.noreply.github.com>

Closes #17825 from zero323/SPARK-20550.

R/pkg/R/DataFrame.R

@@ -3745,3 +3745,27 @@ setMethod("hint",
             jdf <- callJMethod(x@sdf, "hint", name, parameters)
             dataFrame(jdf)
           })
+
+#' alias
+#'
+#' @aliases alias,SparkDataFrame-method
+#' @family SparkDataFrame functions
+#' @rdname alias
+#' @name alias
+#' @export
+#' @examples
+#' \dontrun{
+#' df <- alias(createDataFrame(mtcars), "mtcars")
+#' avg_mpg <- alias(agg(groupBy(df, df$cyl), avg(df$mpg)), "avg_mpg")
+#'
+#' head(select(df, column("mtcars.mpg")))
+#' head(join(df, avg_mpg, column("mtcars.cyl") == column("avg_mpg.cyl")))
+#' }
+#' @note alias(SparkDataFrame) since 2.3.0
+setMethod("alias",
+          signature(object = "SparkDataFrame"),
+          function(object, data) {
+            stopifnot(is.character(data))
+            sdf <- callJMethod(object@sdf, "alias", data)
+            dataFrame(sdf)
+          })

R/pkg/R/column.R

@@ -130,19 +130,19 @@ createMethods <- function() {
 
 createMethods()
 
-#' alias
-#'
-#' Set a new name for a column
-#'
-#' @param object Column to rename
-#' @param data new name to use
-#'
 #' @rdname alias
 #' @name alias
 #' @aliases alias,Column-method
 #' @family colum_func
 #' @export
-#' @note alias since 1.4.0
+#' @examples \dontrun{
+#' df <- createDataFrame(iris)
+#'
+#' head(select(
+#'   df, alias(df$Sepal_Length, "slength"), alias(df$Petal_Length, "plength")
+#' ))
+#' }
+#' @note alias(Column) since 1.4.0
 setMethod("alias",
           signature(object = "Column"),
           function(object, data) {

R/pkg/R/generics.R

@@ -387,6 +387,17 @@ setGeneric("value", function(bcast) { standardGeneric("value") })
 #' @export
 setGeneric("agg", function (x, ...) { standardGeneric("agg") })
 
+#' alias
+#'
+#' Returns a new SparkDataFrame or a Column with an alias set. Equivalent to SQL "AS" keyword.
+#'
+#' @name alias
+#' @rdname alias
+#' @param object x a SparkDataFrame or a Column
+#' @param data new name to use
+#' @return a SparkDataFrame or a Column
+NULL
+
 #' @rdname arrange
 #' @export
 setGeneric("arrange", function(x, col, ...) { standardGeneric("arrange") })

R/pkg/inst/tests/testthat/test_sparkSQL.R

@@ -1223,6 +1223,16 @@ test_that("select with column", {
   expect_equal(columns(df4), c("name", "age"))
   expect_equal(count(df4), 3)
 
+  # Test select with alias
+  df5 <- alias(df, "table")
+
+  expect_equal(columns(select(df5, column("table.name"))), "name")
+  expect_equal(columns(select(df5, "table.name")), "name")
+
+  # Test that stats::alias is not masked
+  expect_is(alias(aov(yield ~ block + N * P * K, npk)), "listof")
+
+
   expect_error(select(df, c("name", "age"), "name"),
                 "To select multiple columns, use a character vector or list for col")
 })