[SPARK-16128][SQL] Allow setting length of characters to be truncated to, in Dataset.show function.

## What changes were proposed in this pull request?

Allowing truncate to a specific number of character is convenient at times, especially while operating from the REPL. Sometimes those last few characters make all the difference, and showing everything brings in whole lot of noise.

## How was this patch tested?
Existing tests. + 1 new test in DataFrameSuite.

For SparkR and pyspark, existing tests and manual testing.

Author: Prashant Sharma <prashsh1@in.ibm.com>
Author: Prashant Sharma <prashant@apache.org>

Closes #13839 from ScrapCodes/add_truncateTo_DF.show.

1 files changed, 15 insertions, 3 deletions

diff --git a/python/pyspark/sql/dataframe.py b/python/pyspark/sql/dataframe.py
index acf9d08b23..a2443ed3d6 100644
--- a/python/pyspark/sql/dataframe.py
+++ b/python/pyspark/sql/dataframe.py
@@ -271,7 +271,9 @@ class DataFrame(object):
         """Prints the first ``n`` rows to the console.
 
         :param n: Number of rows to show.
-        :param truncate: Whether truncate long strings and align cells right.
+        :param truncate: If set to True, truncate strings longer than 20 chars by default.
+            If set to a number greater than one, truncates long strings to length ``truncate``
+            and align cells right.
 
         >>> df
         DataFrame[age: int, name: string]
@@ -282,8 +284,18 @@ class DataFrame(object):
         |  2|Alice|
         |  5|  Bob|
         +---+-----+
-        """
-        print(self._jdf.showString(n, truncate))
+        >>> df.show(truncate=3)
+        +---+----+
+        |age|name|
+        +---+----+
+        |  2| Ali|
+        |  5| Bob|
+        +---+----+
+        """
+        if isinstance(truncate, bool) and truncate:
+            print(self._jdf.showString(n, 20))
+        else:
+            print(self._jdf.showString(n, int(truncate)))
 
     def __repr__(self):
         return "DataFrame[%s]" % (", ".join("%s: %s" % c for c in self.dtypes))