在PySpark中,對於RDD的每個元素,我試圖獲得一個元素的數組。然後我想將結果轉換爲DataFrame。無法在RDD上應用flatMap
我有以下代碼:
simulation = housesDF.flatMap(lambda house: goThroughAB(jobId, house))
print simulation.toDF().show()
在那,我調用這些輔助方法:
def simulate(jobId, house, a, b):
return Row(jobId=jobId, house=house, a=a, b=b, myVl=[i for i in range(10)])
def goThroughAB(jobId, house):
print "in goThroughAB"
results = []
for a in as:
for b in bs:
results += simulate(jobId, house, a, b)
print type(results)
return results
奇怪的是print "in goThroughAB"
沒有任何影響,因爲有上沒有輸出屏幕。
不過,我得到這個錯誤:
---> 23 print simulation.toDF().show()
24
25 dfRow = sqlContext.createDataFrame(simulationResults)
/databricks/spark/python/pyspark/sql/context.py in toDF(self, schema, sampleRatio)
62 [Row(name=u'Alice', age=1)]
63 """
---> 64 return sqlContext.createDataFrame(self, schema, sampleRatio)
65
66 RDD.toDF = toDF
/databricks/spark/python/pyspark/sql/context.py in createDataFrame(self, data, schema, samplingRatio)
421
422 if isinstance(data, RDD):
--> 423 rdd, schema = self._createFromRDD(data, schema, samplingRatio)
424 else:
425 rdd, schema = self._createFromLocal(data, schema)
/databricks/spark/python/pyspark/sql/context.py in _createFromRDD(self, rdd, schema, samplingRatio)
308 """
309 if schema is None or isinstance(schema, (list, tuple)):
--> 310 struct = self._inferSchema(rdd, samplingRatio)
311 converter = _create_converter(struct)
312 rdd = rdd.map(converter)
/databricks/spark/python/pyspark/sql/context.py in _inferSchema(self, rdd, samplingRatio)
261
262 if samplingRatio is None:
--> 263 schema = _infer_schema(first)
264 if _has_nulltype(schema):
265 for row in rdd.take(100)[1:]:
/databricks/spark/python/pyspark/sql/types.py in _infer_schema(row)
829
830 else:
--> 831 raise TypeError("Can not infer schema for type: %s" % type(row))
832
833 fields = [StructField(k, _infer_type(v), True) for k, v in items]
TypeError: Can not infer schema for type: <type 'str'>
在此行中:
print simulation.toDF().show()
所以看起來不執行goThroughAB
,這意味着flatMap
可能不會被執行。
代碼的問題是什麼?
打印語句是在分佈式環境中毫無用處。而這個問題也沒有例子'住宅DF'。 – zero323