[SPARK-14639] [PYTHON] [R] Add `bround` function in Python/R.

## What changes were proposed in this pull request?

This issue aims to expose Scala `bround` function in Python/R API.
`bround` function is implemented in SPARK-14614 by extending current `round` function.
We used the following semantics from Hive.
```java
public static double bround(double input, int scale) {
    if (Double.isNaN(input) || Double.isInfinite(input)) {
      return input;
    }
    return BigDecimal.valueOf(input).setScale(scale, RoundingMode.HALF_EVEN).doubleValue();
}
```

After this PR, `pyspark` and `sparkR` also support `bround` function.

**PySpark**
```python
>>> from pyspark.sql.functions import bround
>>> sqlContext.createDataFrame([(2.5,)], ['a']).select(bround('a', 0).alias('r')).collect()
[Row(r=2.0)]
```

**SparkR**
```r
> df = createDataFrame(sqlContext, data.frame(x = c(2.5, 3.5)))
> head(collect(select(df, bround(df$x, 0))))
  bround(x, 0)
1            2
2            4
```

## How was this patch tested?

Pass the Jenkins tests (including new testcases).

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12509 from dongjoon-hyun/SPARK-14639.

1 files changed, 21 insertions, 1 deletions

diff --git a/R/pkg/R/functions.R b/R/pkg/R/functions.R
index db877b2d63..54234b0455 100644
--- a/R/pkg/R/functions.R
+++ b/R/pkg/R/functions.R
@@ -994,7 +994,7 @@ setMethod("rint",
 
 #' round
 #'
-#' Returns the value of the column `e` rounded to 0 decimal places.
+#' Returns the value of the column `e` rounded to 0 decimal places using HALF_UP rounding mode.
 #'
 #' @rdname round
 #' @name round
@@ -1008,6 +1008,26 @@ setMethod("round",
             column(jc)
           })
 
+#' bround
+#'
+#' Returns the value of the column `e` rounded to `scale` decimal places using HALF_EVEN rounding
+#' mode if `scale` >= 0 or at integral part when `scale` < 0.
+#' Also known as Gaussian rounding or bankers' rounding that rounds to the nearest even number.
+#' bround(2.5, 0) = 2, bround(3.5, 0) = 4.
+#'
+#' @rdname bround
+#' @name bround
+#' @family math_funcs
+#' @export
+#' @examples \dontrun{bround(df$c, 0)}
+setMethod("bround",
+          signature(x = "Column"),
+          function(x, scale = 0) {
+            jc <- callJStatic("org.apache.spark.sql.functions", "bround", x@jc, as.integer(scale))
+            column(jc)
+          })
+
+
 #' rtrim
 #'
 #' Trim the spaces from right end for the specified string value.