[SPARK-10075] [SPARKR] Add `when` expressino function in SparkR

- Add `when` and `otherwise` as `Column` methods
- Add `When` as an expression function
- Add `%otherwise%` infix as an alias of `otherwise`

Since R doesn't support a feature like method chaining, `otherwise(when(condition, value), value)` style is a little annoying for me. If `%otherwise%` looks strange for shivaram, I can remove it. What do you think?

### JIRA
[[SPARK-10075] Add `when` expressino function in SparkR - ASF JIRA](https://issues.apache.org/jira/browse/SPARK-10075)

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #8266 from yu-iskw/SPARK-10075.

1 files changed, 7 insertions, 0 deletions

diff --git a/R/pkg/inst/tests/test_sparkSQL.R b/R/pkg/inst/tests/test_sparkSQL.R
index 83caba8b5b..841de657df 100644
--- a/R/pkg/inst/tests/test_sparkSQL.R
+++ b/R/pkg/inst/tests/test_sparkSQL.R
@@ -727,6 +727,13 @@ test_that("greatest() and least() on a DataFrame", {
   expect_equal(collect(select(df, least(df$a, df$b)))[, 1], c(1, 3))
 })
 
+test_that("when() and otherwise() on a DataFrame", {
+  l <- list(list(a = 1, b = 2), list(a = 3, b = 4))
+  df <- createDataFrame(sqlContext, l)
+  expect_equal(collect(select(df, when(df$a > 1 & df$b > 2, 1)))[, 1], c(NA, 1))
+  expect_equal(collect(select(df, otherwise(when(df$a > 1, 1), 0)))[, 1], c(0, 1))
+})
+
 test_that("group by", {
   df <- jsonFile(sqlContext, jsonPath)
   df1 <- agg(df, name = "max", age = "sum")