[SPARK-10904] [SPARKR] Fix to support select(df, c("col1", "col2"))

The fix is to coerce `c("a", "b")` into a list such that it could be serialized to call JVM with.

Author: felixcheung <felixcheung_m@hotmail.com>

Closes #8961 from felixcheung/rselect.

(cherry picked from commit 721e8b5)
Signed-off-by: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

R/pkg/R/DataFrame.R

@@ -1044,12 +1044,20 @@ setMethod("subset", signature(x = "DataFrame"),
 #'   select(df, c("col1", "col2"))
 #'   select(df, list(df$name, df$age + 1))
 #'   # Similar to R data frames columns can also be selected using `$`
-#'   df$age
+#'   df[,df$age]
 #' }
 setMethod("select", signature(x = "DataFrame", col = "character"),
           function(x, col, ...) {
-            sdf <- callJMethod(x@sdf, "select", col, toSeq(...))
-            dataFrame(sdf)
+            if (length(col) > 1) {
+              if (length(list(...)) > 0) {
+                stop("To select multiple columns, use a character vector or list for col")
+              }
+
+              select(x, as.list(col))
+            } else {
+              sdf <- callJMethod(x@sdf, "select", col, toSeq(...))
+              dataFrame(sdf)
+            }
           })
 
 #' @rdname select

R/pkg/inst/tests/test_sparkSQL.R

@@ -585,6 +585,13 @@ test_that("select with column", {
   expect_equal(columns(df3), c("x"))
   expect_equal(count(df3), 3)
   expect_equal(collect(select(df3, "x"))[[1, 1]], "x")
+
+  df4 <- select(df, c("name", "age"))
+  expect_equal(columns(df4), c("name", "age"))
+  expect_equal(count(df4), 3)
+
+  expect_error(select(df, c("name", "age"), "name"),
+                "To select multiple columns, use a character vector or list for col")
 })
 
 test_that("subsetting", {