HyukjinKwon commented on a change in pull request #23534: [SPARK-26610][PYTHON]
Fix inconsistency between toJSON Method in Python and Scala.
URL: https://github.com/apache/spark/pull/23534#discussion_r247455277
##########
File path: python/pyspark/sql/dataframe.py
##########
@@ -109,15 +109,18 @@ def stat(self):
@ignore_unicode_prefix
@since(1.3)
def toJSON(self, use_unicode=True):
- """Converts a :class:`DataFrame` into a :class:`RDD` of string.
+ """Converts a :class:`DataFrame` into a :class:`DataFrame` of JSON
string.
- Each row is turned into a JSON document as one element in the returned
RDD.
+ Each row is turned into a JSON document as one element in the returned
DataFrame.
>>> df.toJSON().first()
- u'{"age":2,"name":"Alice"}'
+ Row(value=u'{"age":2,"name":"Alice"}')
"""
- rdd = self._jdf.toJSON()
- return RDD(rdd.toJavaRDD(), self._sc, UTF8Deserializer(use_unicode))
+ jdf = self._jdf.toJSON()
+ if self.sql_ctx._conf.pysparkDataFrameToJSONShouldReturnDataFrame():
+ return DataFrame(jdf, self.sql_ctx)
+ else:
+ return RDD(jdf.toJavaRDD(), self._sc,
UTF8Deserializer(use_unicode))
Review comment:
The problem is, the API usage is different. You can directly do, for
instance, `map` on what `toJSON` returns for instance.
```python
spark.range(1).toJSON().map(lambda value: value + "abc")
```
now it should be something like
```python
spark.range(1).toJSON().selectExpr("concat(_1, 'abc')")
```
This is pretty inconsistent with Scala side. I don't think we could say this
is consistent since Dataset itself can be a replacement of an RDD but DataFrame
is not.
For instance, `DataFrameReader.csv` or `DataFrameReader.json` doesn't accept
`DataFrame` as an input because Scala side takes `Dataset[String]`. It only
takes RDD.
```python
>>> spark.read.json(spark.range(1).toJSON()).show()
```
```
+---+
| id|
+---+
| 0|
+---+
```
```python
>>> spark.read.json(spark.range(1)).show()
```
```
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/.../spark/python/pyspark/sql/readwriter.py", line 293, in json
raise TypeError("path can be only string, list or RDD")
TypeError: path can be only string, list or RDD
```
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