[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, 16 insertions, 3 deletions

diff --git a/python/pyspark/sql/functions.py b/python/pyspark/sql/functions.py
index 5017ab5b36..dac842c0ce 100644
--- a/python/pyspark/sql/functions.py
+++ b/python/pyspark/sql/functions.py
@@ -467,16 +467,29 @@ def randn(seed=None):
 @since(1.5)
 def round(col, scale=0):
     """
-    Round the value of `e` to `scale` decimal places if `scale` >= 0
+    Round the given value to `scale` decimal places using HALF_UP rounding mode if `scale` >= 0
     or at integral part when `scale` < 0.
 
-    >>> sqlContext.createDataFrame([(2.546,)], ['a']).select(round('a', 1).alias('r')).collect()
-    [Row(r=2.5)]
+    >>> sqlContext.createDataFrame([(2.5,)], ['a']).select(round('a', 0).alias('r')).collect()
+    [Row(r=3.0)]
     """
     sc = SparkContext._active_spark_context
     return Column(sc._jvm.functions.round(_to_java_column(col), scale))
 
 
+@since(2.0)
+def bround(col, scale=0):
+    """
+    Round the given value to `scale` decimal places using HALF_EVEN rounding mode if `scale` >= 0
+    or at integral part when `scale` < 0.
+
+    >>> sqlContext.createDataFrame([(2.5,)], ['a']).select(bround('a', 0).alias('r')).collect()
+    [Row(r=2.0)]
+    """
+    sc = SparkContext._active_spark_context
+    return Column(sc._jvm.functions.bround(_to_java_column(col), scale))
+
+
 @since(1.5)
 def shiftLeft(col, numBits):
     """Shift the given value numBits left.