Re: How to change a DataFrame column from nullable to not nullable in PySpark

[Mich Talebzadeh]

Spark allows one to define the column format as StructType or list. By
default Spark assumes that all fields are nullable when creating a
dataframe.

To change nullability you need to provide the structure of the columns.

Assume that I have created an RDD in the form

rdd = sc.parallelize(Range). \
         map(lambda x: (x, usedFunctions.clustered(x,numRows), \
                           usedFunctions.scattered(x,numRows), \
                           usedFunctions.randomised(x,numRows), \
                           usedFunctions.randomString(50), \
                           usedFunctions.padString(x," ",50), \
                           usedFunctions.padSingleChar("x",4000)))

For the above I create a schema with StructType as below:

Schema = StructType([ *StructField("ID", IntegerType(), False*),
                      StructField("CLUSTERED", FloatType(), True),
                      StructField("SCATTERED", FloatType(), True),
                      StructField("RANDOMISED", FloatType(), True),
                      StructField("RANDOM_STRING", StringType(), True),
                      StructField("SMALL_VC", StringType(), True),
                      StructField("PADDING", StringType(), True)
                    ])

Note that the first column ID is defined as  NOT NULL

Then I can create a dataframe df as below

df= spark.createDataFrame(rdd, schema = Schema)
df.printSchema()

root
 |-- ID: integer (nullable = false)
 |-- CLUSTERED: float (nullable = true)
 |-- SCATTERED: float (nullable = true)
 |-- RANDOMISED: float (nullable = true)
 |-- RANDOM_STRING: string (nullable = true)
 |-- SMALL_VC: string (nullable = true)
 |-- PADDING: string (nullable = true)


HTH


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On Thu, 14 Oct 2021 at 12:50, ashok34...@yahoo.com.INVALID
<ashok34...@yahoo.com.invalid> wrote:

> Gurus,
>
> I have an RDD in PySpark that I can convert to DF through
>
> df = rdd.toDF()
>
> However, when I do
>
> df.printSchema()
>
> I see the columns as nullable. = true by default
>
> root
>  |-- COL-1: long (nullable = true)
>  |-- COl-2: double (nullable = true)
>  |-- COl-3: string (nullable = true)
>
> What would be the easiest way to make COL-1 NOT NULLABLE
>
> Thanking you
>