主要目标
显示或选择从拼花文件读取的Spark数据框中的列。
论坛中提到的所有解决方案在我们的案例中都不成功
问题
当使用SPARK读取和查询拼花地板文件时,会出现此问题,这是由于列名中存在特殊字符 ,;{}()\n\t=
。这个问题是用一个简单的拼花文件重现的,它有两列五行。列的名称为:
SpeedReference_Final_01 (RifVel_G0)
SpeedReference_Final_02 (RifVel_G1)
出现的错误是:Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
我们正在Python语言中使用PySpark,实验解决方案可分为以下几类:
基于列重命名的解决方案-[spark.read.parquet
+获得的数据帧的重命名]
已经试验了几种解决方案:
withColumnRenamed
(脚本中的问题N.2)toDF
(第3期)alias
(第5期)他们中没有一个在我们的案件中起作用
将拼花地板文件读入熊猫数据框,然后从中创建一个新的拼花地板文件-[pd.read.parquet
+spark.createDataFrame
]
此解决方案使用的是一个小拼花文件(问题N.0,即脚本中的解决方法):即使创建的spark dataframe具有包含特殊字符的列名,也可以成功查询它不幸的是,对于我们的大型拼花文件(每个拼花600000行x 1000列),这是不可行的,因为创建spark数据框是无止境的
尝试将拼花地板文件读入Spark数据框,并使用其rdd
和重命名的模式创建新的Spark数据框是不可行的,因为从Spark数据框提取rdd
会产生相同的错误(问题N.4)
读取带有前缀模式的拼花地板文件(避免特殊字符)-[spark.read.schema(...).parquet
]
由于原始文件中不存在重命名的列,因此与关键列相关的数据按预期变为null/None,因此解决方案不起作用
下面的python代码总结了提到的解决方案,并用Example parquet file进行了实验
from pyspark.sql import SparkSession
from pyspark.sql.types import *
from pyspark.sql.functions import col
import pandas as pd
spark = SparkSession \
.builder \
.appName("Python Spark SQL basic example") \
.config("spark.some.config.option", "some-value") \
.getOrCreate()
# Select file
filename = 'D:/Simple.parquet'
issue_num = 0 # Workaround to issues (Equivalent to no issue)
#issue_num = 1 # Issue 1 - Unable to show dataframe or select column with name containing invalid character(s)
#issue_num = 2 # Issue 2 - Unable to show dataframe or select column after rename (using withColumnRenamed)
#issue_num = 3 # Issue 3 - Unable to show dataframe or select column after rename (using toDF)
#issue_num = 4 # Issue 4 - Unable to extract rdd from renamed dataframe
#issue_num = 5 # Issue 5 - Unable to select column with alias
if issue_num == 0:
################################################################################################
# WORKAROUND - Create Spark data frame from Pandas dataframe
df_pd = pd.read_parquet(filename)
DF = spark.createDataFrame(df_pd)
print('WORKAROUND')
DF.show()
# +-----------------------------------+-----------------------------------+
# |SpeedReference_Final_01 (RifVel_G0)|SpeedReference_Final_02 (RifVel_G1)|
# +-----------------------------------+-----------------------------------+
# | 553.5228271484375| 720.3720703125|
# | 553.5228271484375| 720.3720703125|
# | 553.5228271484375| 720.3720703125|
# | 553.5228271484375| 720.3720703125|
# | 553.5228271484375| 720.3720703125|
# +-----------------------------------+-----------------------------------+
################################################################################################
# Correct management of columns with invalid characters when using spark.createDataFrame
# spark.createDataFrame: Create a dataframe with two columns with invalid characters - OK
# DFCREATED
schema = StructType(
[
StructField("SpeedReference_Final_01 (RifVel_G0)", FloatType(), nullable=True),
StructField("SpeedReference_Final_02 (RifVel_G1)", FloatType(), nullable=True)
]
)
row_in = [(553.523,720.372), (553.523,720.372), (553.523,720.372), (553.523,720.372), (553.523,720.372)]
rdd=spark.sparkContext.parallelize(row_in)
DFCREATED = spark.createDataFrame(rdd, schema)
DFCREATED.show()
# +-----------------------------------+-----------------------------------+
# |SpeedReference_Final_01 (RifVel_G0)|SpeedReference_Final_02 (RifVel_G1)|
# +-----------------------------------+-----------------------------------+
# | 553.523| 720.372|
# | 553.523| 720.372|
# | 553.523| 720.372|
# | 553.523| 720.372|
# | 553.523| 720.372|
# +-----------------------------------+-----------------------------------+
DF_SEL_VAR_CREATED = DFCREATED.select(DFCREATED.columns[0]).take(2)
for el in DF_SEL_VAR_CREATED:
print(el)
#Row(SpeedReference_Final_01 (RifVel_G0)=553.5230102539062)
#Row(SpeedReference_Final_01 (RifVel_G0)=553.5230102539062)
else:
# spark.read: read file into dataframe - OK
DF = spark.read.parquet(filename)
print('ORIGINAL SCHEMA')
DF.printSchema()
# root
# |-- SpeedReference_Final_01 (RifVel_G0): float (nullable = true)
# |-- SpeedReference_Final_02 (RifVel_G1): float (nullable = true)
if issue_num == 1:
###############################################################################################
# Issue 1 - Unable to show dataframe or select column with name containing invalid character(s)
DF.show()
# DF.select(DF.columns[0]).show()
# DF_SEL_VAR = DF.select(DF.columns[0]).take(3)
#ECC: Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
# on all 3 previous statements
elif issue_num == 2:
###############################################################################################
# Issue 2 - Unable to show dataframe or select column after rename (using withColumnRenamed)
DFRENAMED = DF.withColumnRenamed('SpeedReference_Final_01 (RifVel_G0)','RifVelG0').withColumnRenamed('SpeedReference_Final_02 (RifVel_G1)','RifVelG1')
print('RENAMED SCHEMA')
DFRENAMED.printSchema()
# root
# |-- RifVelG0: float (nullable = true)
# |-- RifVelG1: float (nullable = true)
DFRENAMED.show()
# DF_SEL_VAR_RENAMED = DFRENAMED.select(DFRENAMED.RifVelG0).take(2)
#ECC: Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
# on all 2 previous statements
elif issue_num == 3:
###############################################################################################
# Issue 3 - Unable to show dataframe or select column after rename (using to_DF)
DFRENAMED = DF.toDF('RifVelG0', 'RifVelG1')
print('RENAMED SCHEMA')
DFRENAMED.printSchema()
# root
# |-- RifVelG0: float (nullable = true)
# |-- RifVelG1: float (nullable = true)
DFRENAMED.show()
# DF_SEL_VAR_RENAMED = DFRENAMED.select(DFRENAMED.RifVelG0).take(2)
#ECC: Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
# on all 2 previous statements
elif issue_num == 4:
###############################################################################################
# Issue 4 - Unable to extract rdd from renamed dataframe
DFRENAMED = DF.withColumnRenamed('SpeedReference_Final_01 (RifVel_G0)','RifVelG0').withColumnRenamed('SpeedReference_Final_02 (RifVel_G1)','RifVelG1')
DFRENAMED_rdd = DFRENAMED.rdd
#ECC: Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
elif issue_num == 5:
###############################################################################################
# Issue 5 - Unable to select column with alias
DF_SEL_VAR = DF.select(col(DF.columns[0]).alias('RifVelG0')).take(3)
#ECC: Attribute name "SpeedReference_Final_01 (RifVel_G0)" contains invalid character(s) among " ,;{}()\n\t=". Please use alias to rename it.
你知道我们怎样才能解决这个问题吗
任何建议都非常感谢
目前没有回答
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