为什么 dropna() 不起作用？

系统：Cloudera Quickstart VM 5.4 上的 Spark 1.3.0（Anaconda Python 版本）

这是一个 Spark 数据框：

from pyspark.sql import SQLContext
from pyspark.sql.types import *
sqlContext = SQLContext(sc)

data = sc.parallelize([('Foo',41,'US',3),
                       ('Foo',39,'UK',1),
                       ('Bar',57,'CA',2),
                       ('Bar',72,'CA',3),
                       ('Baz',22,'US',6),
                       (None,75,None,7)])

schema = StructType([StructField('Name', StringType(), True),
                     StructField('Age', IntegerType(), True),
                     StructField('Country', StringType(), True),
                     StructField('Score', IntegerType(), True)])

df = sqlContext.createDataFrame(data,schema)

data.show()

Name Age Country Score
Foo  41  US      3    
Foo  39  UK      1    
Bar  57  CA      2    
Bar  72  CA      3    
Baz  22  US      6    
null 75  null    7 

然而这些都不起作用！

df.dropna()
df.na.drop()

我收到这条消息：

>>> df.show()
Name Age Country Score
Foo  41  US      3    
Foo  39  UK      1    
Bar  57  CA      2    
Bar  72  CA      3    
Baz  22  US      6    
null 75  null    7    
>>> df.dropna().show()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/spark/python/pyspark/sql/dataframe.py", line 580, in __getattr__
    jc = self._jdf.apply(name)
  File "/usr/lib/spark/python/lib/py4j-0.8.2.1-src.zip/py4j/java_gateway.py", line 538, in __call__
  File "/usr/lib/spark/python/lib/py4j-0.8.2.1-src.zip/py4j/protocol.py", line 300, in get_return_value
py4j.protocol.Py4JJavaError: An error occurred while calling o50.apply.
: org.apache.spark.sql.AnalysisException: Cannot resolve column name "dropna" among (Name, Age, Country, Score);
    at org.apache.spark.sql.DataFrame$$anonfun$resolve$1.apply(DataFrame.scala:162)
    at org.apache.spark.sql.DataFrame$$anonfun$resolve$1.apply(DataFrame.scala:162)
    at scala.Option.getOrElse(Option.scala:120)
    at org.apache.spark.sql.DataFrame.resolve(DataFrame.scala:161)
    at org.apache.spark.sql.DataFrame.col(DataFrame.scala:436)
    at org.apache.spark.sql.DataFrame.apply(DataFrame.scala:426)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:379)
    at py4j.Gateway.invoke(Gateway.java:259)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:207)
    at java.lang.Thread.run(Thread.java:745)

还有其他人遇到过这个问题吗？解决方法是什么？ Pyspark 似乎认为我正在寻找一个名为“na”的专栏。任何帮助，将不胜感激！

tl;dr方法na and dropna仅从 Spark 1.3.1 起可用。

你犯过的几个错误：

1. data = sc.parallelize([....('',75,'', 7 )])，您打算使用''代表None，但是，它只是一个 String 而不是 null

2. na and dropna都是 dataFrame 类上的方法，因此，您应该用您的df.

可运行代码：

data = sc.parallelize([('Foo',41,'US',3),
                       ('Foo',39,'UK',1),
                       ('Bar',57,'CA',2),
                       ('Bar',72,'CA',3),
                       ('Baz',22,'US',6),
                       (None, 75, None, 7)])

schema = StructType([StructField('Name', StringType(), True),
                 StructField('Age', IntegerType(), True),
                 StructField('Country', StringType(), True),
                 StructField('Score', IntegerType(), True)])

df = sqlContext.createDataFrame(data,schema)

df.dropna().show()
df.na.drop().show()