[SPARK-19682][SPARKR] Issue warning (or error) when subset method "[[" takes vector index

## What changes were proposed in this pull request?
The `[[` method is supposed to take a single index and return a column. This is different from base R which takes a vector index.  We should check for this and issue warning or error when vector index is supplied (which is very likely given the behavior in base R).

Currently I'm issuing a warning message and just take the first element of the vector index. We could change this to an error it that's better.

## How was this patch tested?
new tests

Author: actuaryzhang <actuaryzhang10@gmail.com>

Closes #17017 from actuaryzhang/sparkRSubsetter.

1 files changed, 12 insertions, 0 deletions

diff --git a/R/pkg/inst/tests/testthat/test_sparkSQL.R b/R/pkg/inst/tests/testthat/test_sparkSQL.R
index a7259f362e..ce0f5a198a 100644
--- a/R/pkg/inst/tests/testthat/test_sparkSQL.R
+++ b/R/pkg/inst/tests/testthat/test_sparkSQL.R
@@ -1015,6 +1015,18 @@ test_that("select operators", {
   expect_is(df[[2]], "Column")
   expect_is(df[["age"]], "Column")
 
+  expect_warning(df[[1:2]],
+                 "Subset index has length > 1. Only the first index is used.")
+  expect_is(suppressWarnings(df[[1:2]]), "Column")
+  expect_warning(df[[c("name", "age")]],
+                 "Subset index has length > 1. Only the first index is used.")
+  expect_is(suppressWarnings(df[[c("name", "age")]]), "Column")
+
+  expect_warning(df[[1:2]] <- df[[1]],
+                 "Subset index has length > 1. Only the first index is used.")
+  expect_warning(df[[c("name", "age")]] <- df[[1]],
+                 "Subset index has length > 1. Only the first index is used.")
+
   expect_is(df[, 1, drop = F], "SparkDataFrame")
   expect_equal(columns(df[, 1, drop = F]), c("name"))
   expect_equal(columns(df[, "age", drop = F]), c("age"))