我需要为id字段生成自动递增的值。我的方法是使用windows函数和max函数。
我试图找到纯数据帧解决方案(没有rdd)。
所以在我right-outer join
之后我得到了这个数据帧:
df2 = sqlContext.createDataFrame([(1,2), (3, None), (5, None)], ['someattr', 'id'])
# notice null values? it's a new records that don't have id just yet.
# The task is to generate them. Preferably with one query.
df2.show()
+--------+----+
|someattr| id|
+--------+----+
| 1| 2|
| 3|null|
| 5|null|
+--------+----+
我需要为id
字段生成自动递增的值。我的方法是使用Windows函数
df2.withColumn('id', when(df2.id.isNull(), row_number().over(Window.partitionBy('id').orderBy('id')) + max('id')).otherwise(df2.id))
当我这样做时,它会引发异常:
AnalysisException Traceback (most recent call last)
<ipython-input-102-b3221098e895> in <module>()
10
11
---> 12 df2.withColumn('hello', when(df2.id.isNull(), row_number().over(Window.partitionBy('id').orderBy('id')) + max('id')).otherwise(df2.id)).show()
/Users/ipolynets/workspace/spark-2.0.0/python/pyspark/sql/dataframe.pyc in withColumn(self, colName, col)
1371 """
1372 assert isinstance(col, Column), "col should be Column"
-> 1373 return DataFrame(self._jdf.withColumn(colName, col._jc), self.sql_ctx)
1374
1375 @ignore_unicode_prefix
/Users/ipolynets/workspace/spark-2.0.0/python/lib/py4j-0.10.1-src.zip/py4j/java_gateway.py in __call__(self, *args)
931 answer = self.gateway_client.send_command(command)
932 return_value = get_return_value(
--> 933 answer, self.gateway_client, self.target_id, self.name)
934
935 for temp_arg in temp_args:
/Users/ipolynets/workspace/spark-2.0.0/python/pyspark/sql/utils.pyc in deco(*a, **kw)
67 e.java_exception.getStackTrace()))
68 if s.startswith('org.apache.spark.sql.AnalysisException: '):
---> 69 raise AnalysisException(s.split(': ', 1)[1], stackTrace)
70 if s.startswith('org.apache.spark.sql.catalyst.analysis'):
71 raise AnalysisException(s.split(': ', 1)[1], stackTrace)
AnalysisException: u"expression '`someattr`' is neither present in the group by, nor is it an aggregate function. Add to group by or wrap in first() (or first_value) if you don't care which value you get.;"
不确定这个例外抱怨说实话。
请注意我如何将window
函数添加到常规max()
函数?
row_number().over(Window.partitionBy('id').orderBy('id')) + max('id')
我不确定是否允许这样做。
哦......这是期望查询的预期输出。你可能已经想过了。
+--------+----+
|someattr| id|
+--------+----+
| 1| 2|
| 3| 3|
| 5| 4|
+--------+----+
答案 0 :(得分:1)
您正在添加列,因此在结果DataFrame中还会有someattr
列。
您必须在someattr
中加入group by
或在某些汇总功能中使用它。
但是,这样做更简单:
df2.registerTempTable("test")
df3 = sqlContext.sql("""
select t.someattr, nvl (t.id, row_number(partition by id) over () + maxId.maxId) as id
from test t
cross join (select max(id) as maxId from test) as maxId
""")
当然,您可以将其转换为DSL,但对于我来说,SQL对于此任务来说似乎更容易