我有 train_rdd 就像 (('a',1),('b',2),('c',3)) . 我使用以下方法将其转换为Dataframe

from pyspark.sql import Row
train_label_df = train_rdd.map(lambda x: (Row(**dict(x)))).toDF()

但也许某些RDD中缺少一些密钥。所以会出现错误。

File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000017/pyspark.zip/pyspark/worker.py", line
253, in main
process()
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000017/pyspark.zip/pyspark/worker.py", line
248, in process
serializer.dump_stream(func(split_index, iterator), outfile)
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000002/pyspark.zip/pyspark/rdd.py", line
2440, in pipeline_func
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000002/pyspark.zip/pyspark/rdd.py", line
2440, in pipeline_func
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000002/pyspark.zip/pyspark/rdd.py", line
350, in func
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000002/pyspark.zip/pyspark/rdd.py", line
1859, in combineLocally
File
"/mnt/hadoop/yarn/local/usercache/hdfs/appcache/application_/container_05_000017/pyspark.zip/pyspark/shuffle.py", line
237, in mergeValues
for k, v in iterator:
    TypeError: cannot unpack non - iterable NoneType object

有没有其他方法可以将元组类型rdd转换为Dataframe？
更新：
我也试着用 createDataFrame .

rdd = sc.parallelize([('a',1), (('a',1), ('b',2)), (('a',1), ('b',2), ('c',3) ) ])
schema = StructType([
        StructField("a", StringType(), True),
        StructField("b", StringType(), True),
        StructField("c", StringType(), True),
])
train_label_df = sqlContext.createDataFrame(rdd,  schema)
train_label_df.show()

出现错误。

File "/home/spark/python/pyspark/sql/types.py", line 1400, in verify_struct
    "length of fields (%d)" % (len(obj), len(verifiers))))
ValueError: Length of object (2) does not match with length of fields (3)