Question

执行代码以从HDFS获取spark数据帧然后将其转换为pandas dataframe时，

spark_df = spark.read.parquet(*data_paths)
# other code in the process like filtering, groupby etc.
# ....
# write sparkdf to hadoop, get n rows if specified
        if n:
            spark_df.limit(n).write.csv(tmpfoldername, sep=csv_sep, quote=csv_quote)
        else:
            spark_df.write.csv(tmpfoldername, sep=csv_sep, quote=csv_quote)

我收到错误：

/home/sarah/anaconda3/envs/py27/lib/python2.7/site-packages/dspipeline/core/wf_spark.pyc in to_pd(spark_df, n, save_csv, csv_sep, csv_quote, quick)
    215         # write sparkdf to hadoop, get n rows if specified
    216         if n:
--> 217             spark_df.limit(n).write.csv(tmpfoldername, sep=csv_sep, quote=csv_quote)
    218         else:
    219             spark_df.write.csv(tmpfoldername, sep=csv_sep, quote=csv_quote)

/opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/pyspark/sql/dataframe.py in limit(self, num)
    472         []
    473         """
--> 474         jdf = self._jdf.limit(num)
    475         return DataFrame(jdf, self.sql_ctx)
    476 

/opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/lib/py4j-0.10.4-src.zip/py4j/java_gateway.py in __call__(self, *args)
   1131         answer = self.gateway_client.send_command(command)
   1132         return_value = get_return_value(
-> 1133             answer, self.gateway_client, self.target_id, self.name)
   1134 
   1135         for temp_arg in temp_args:

/opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/pyspark/sql/utils.py in deco(*a, **kw)
     61     def deco(*a, **kw):
     62         try:
---> 63             return f(*a, **kw)
     64         except py4j.protocol.Py4JJavaError as e:
     65             s = e.java_exception.toString()

/opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/lib/py4j-0.10.4-src.zip/py4j/protocol.py in get_return_value(answer, gateway_client, target_id, name)
    321                 raise Py4JError(
    322                     "An error occurred while calling {0}{1}{2}. Trace:\n{3}\n".
--> 323                     format(target_id, ".", name, value))
    324         else:
    325             raise Py4JError(

Py4JError: An error occurred while calling o1086.limit. Trace:
py4j.Py4JException: Method limit([class java.lang.String]) does not exist
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:318)
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:326)
    at py4j.Gateway.invoke(Gateway.java:272)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:214)
    at java.lang.Thread.run(Thread.java:745)

当我在pyspark文档中找到函数limit（num）时，我想原因是我没有正确使用它。有什么帮助吗？

Answer 1

The exception is pretty clear here:

Method limit([class java.lang.String]) does not exist

n you are trying to pass to limit is not an int but a str.

You should go back to the point where n is defined, and fix it.

Answer 2

存在DataFrame的.limit方法，如果要从DataFrame获取n行，则可以使用.limit（n）方法，但是参数n必须为整数。例如：

.a

如果您使用其他参数，例如df.limit(10)，则会发生错误： py4j.Py4JException：方法限制（[class java.lang.String ]）不存在。

Pyspark错误 - py4j.Py4JException：方法限制（[类java.lang.String]）不存在

2 个答案: