PySpark : KeyError when converting a DataFrame column of String type to Double

问题

I'm trying to learn machine learning with PySpark. I have a dataset that has a couple of String columns which have either True or False or Yes or No as its value. I'm working with DecisionTree and I wanted to convert these String values to corresponding Double values i.e. True, Yes should change to 1.0 and False, No should change to 0.0. I saw a tutorial where they did the same thing and I came up with this code

df = sqlContext.read.csv("C:/../churn-bigml-20.csv",inferSchema=True,header=True)

from pyspark.sql.types import DoubleType
from pyspark.sql.functions import UserDefinedFunction

binary_map = {'Yes':1.0, 'No':0.0, 'True':1.0, 'False':0.0}
toNum = UserDefinedFunction(lambda k: binary_map[k], DoubleType())

csv_data = df.drop('State').drop('Area code') \
    .withColumn('Churn', toNum(df['Churn'])) \
    .withColumn('International plan', toNum(df['International plan'])) \
    .withColumn('Voice mail plan', toNum(df['Voice mail plan'])).cache()

However when I run this, I get so many errors that look like this.

  File "C:\..\spark-2.1.0\python\lib\pyspark.zip\pyspark\worker.py", line 70, in <lambda>
  File "C:\..\workspace\PyML\src\ModelBuilding.py", line 20, in <lambda>
    toNum = UserDefinedFunction(lambda k: binary_map[k], DoubleType())
KeyError: False

Note: I'm working on PySpark with Spark 2.1 and Python 3.5 and I guess the tutorial that I follow uses spark 1.6 and Python 2.7. So I don't if this is one of the Python grammar issues.

回答1:

I solved it by changing mapping part to:

binary_map = {'Yes':1.0, 'No':0.0, True : 1.0, False : 0.0}
toNum = UserDefinedFunction(lambda k: binary_map[k], DoubleType())

I just removed the quote from True and False. I thought that was weird but when I checked the schema of the DataFrame using print(df.printSchema()), it showed that the field that has True and False values is of type boolean.

The Schema

root
 |-- State: string (nullable = true)
 |-- Account length: integer (nullable = true)
 |-- Area code: integer (nullable = true)
 |-- International plan: string (nullable = true)
 |-- Voice mail plan: string (nullable = true)
  .
  .
  .
 |-- Customer service calls: integer (nullable = true)
 |-- Churn: boolean (nullable = true)

So that's why I had to take the quotes off. Thank you.

来源：https://stackoverflow.com/questions/43511085/pyspark-keyerror-when-converting-a-dataframe-column-of-string-type-to-double