[SPARK-7687] [SQL] DataFrame.describe() should cast all aggregates to String

In `DataFrame.describe()`, the `count` aggregate produces an integer, the `avg` and `stdev` aggregates produce doubles, and `min` and `max` aggregates can produce varying types depending on what type of column they're applied to.  As a result, we should cast all aggregate results to String so that `describe()`'s output types match its declared output schema.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #6218 from JoshRosen/SPARK-7687 and squashes the following commits:

146b615 [Josh Rosen] Fix R test.
2974bd5 [Josh Rosen] Cast to string type instead
f206580 [Josh Rosen] Cast to double to fix SPARK-7687
307ecbf [Josh Rosen] Add failing regression test for SPARK-7687

1 files changed, 5 insertions, 5 deletions

diff --git a/R/pkg/inst/tests/test_sparkSQL.R b/R/pkg/inst/tests/test_sparkSQL.R
index 3e5658eb5b..1768c57fd0 100644
--- a/R/pkg/inst/tests/test_sparkSQL.R
+++ b/R/pkg/inst/tests/test_sparkSQL.R
@@ -757,12 +757,12 @@ test_that("parquetFile works with multiple input paths", {
 test_that("describe() on a DataFrame", {
   df <- jsonFile(sqlCtx, jsonPath)
   stats <- describe(df, "age")
-  expect_true(collect(stats)[1, "summary"] == "count")
-  expect_true(collect(stats)[2, "age"] == 24.5)
-  expect_true(collect(stats)[3, "age"] == 5.5)
+  expect_equal(collect(stats)[1, "summary"], "count")
+  expect_equal(collect(stats)[2, "age"], "24.5")
+  expect_equal(collect(stats)[3, "age"], "5.5")
   stats <- describe(df)
-  expect_true(collect(stats)[4, "name"] == "Andy")
-  expect_true(collect(stats)[5, "age"] == 30.0)
+  expect_equal(collect(stats)[4, "name"], "Andy")
+  expect_equal(collect(stats)[5, "age"], "30")
 })
 
 unlink(parquetPath)