Spark – How to Change Column Type?

To change the Spark SQL DataFrame column type from one data type to another data type you should use cast() function of Column class, you can use this on withColumn(), select(), selectExpr(), and SQL expression. Note that the type which you want to convert to should be a subclass of DataType class or a string representing the type.

Key points:

  • cast()<a href="https://sparkbyexamples.com/pyspark/pyspark-cast-column-type/">cast()</a> is a function from Column class that is used to convert the column into the other datatype.
  • This function takes the argument string representing the type you wanted to convert or any type that is a subclass of DataType (Below mentioned the types you could cast).
  • When Spark unable to convert into a specific type, it returns a null value.
  • Spark SQL takes the different syntax DOUBLE(String column) to cast types.

ArrayTypeBinaryTypeBooleanTypeCalendarIntervalTypeDateTypeHiveStringTypeMapTypeNullTypeNumericTypeObjectTypeStringTypeStructTypeTimestampType


import org.apache.spark.sql.functions.col
import org.apache.spark.sql.types.IntegerType

// Convert String to Integer Type
df.withColumn("salary",col("salary").cast(IntegerType))
df.withColumn("salary",col("salary").cast("int"))
df.withColumn("salary",col("salary").cast("integer"))

// Using select
df.select(col("salary").cast("int").as("salary"))

//Using selectExpr()
  df.selectExpr("cast(salary as int) salary","isGraduated")
  df.selectExpr("INT(salary)","isGraduated")

//Using with spark.sql()
spark.sql("SELECT INT(salary),BOOLEAN(isGraduated),gender from CastExample")
spark.sql("SELECT cast(salary as int) salary, BOOLEAN(isGraduated),gender from CastExample")

Let’s see some examples here using Scala snippet.

Change Column Type Example

First, let’s create DataFrame.


import org.apache.spark.sql.{Row, SparkSession}
import org.apache.spark.sql.types._
val spark: SparkSession = SparkSession.builder()
    .master("local[1]")
    .appName("SparkByExamples.com")
    .getOrCreate()

val simpleData = Seq(Row("James",34,"2006-01-01","true","M",3000.60),
    Row("Michael",33,"1980-01-10","true","F",3300.80),
    Row("Robert",37,"06-01-1992","false","M",5000.50)
  )

val simpleSchema = StructType(Array(
    StructField("firstName",StringType,true),
    StructField("age",IntegerType,true),
    StructField("jobStartDate",StringType,true),
    StructField("isGraduated", StringType, true),
    StructField("gender", StringType, true),
    StructField("salary", DoubleType, true)
  ))

val df = spark.createDataFrame(
     spark.sparkContext.parallelize(simpleData),simpleSchema)
df.printSchema()
df.show(false)

Outputs:


root
 |-- firstName: string (nullable = true)
 |-- age: integer (nullable = true)
 |-- jobStartDate: string (nullable = true)
 |-- isGraduated: string (nullable = true)
 |-- gender: string (nullable = true)
 |-- salary: double (nullable = true)

+---------+---+------------+-----------+------+------+
|firstName|age|jobStartDate|isGraduated|gender|salary|
+---------+---+------------+-----------+------+------+
|James    |34 |2006-01-01  |true       |M     |3000.6|
|Michael  |33 |1980-01-10  |true       |F     |3300.8|
|Robert   |37 |06-01-1992  |false      |M     |5000.5|
+---------+---+------------+-----------+------+------+

1. Change Column Type using withColumn() and cast()

To convert the data type of a DataFrame column, Use withColumn() with the original column name as a first argument and for the second argument apply the casting method cast() with DataType on the column.

Below Spark, snippet changes DataFrame column, age to String (StringType), isGraduated column from String to Boolean (BooleanType) and ‘jobStartDate‘ column from String to DateType.


import org.apache.spark.sql.functions._
val df2 = df.withColumn("age",col("age").cast(StringType))
    .withColumn("isGraduated",col("isGraduated").cast(BooleanType))
    .withColumn("jobStartDate",col("jobStartDate").cast(DateType))
df2.printSchema()

Outputs:


root
 |-- age: string (nullable = true)
 |-- isGraduated: boolean (nullable = true)
 |-- jobStartDate: date (nullable = true)

3. Using select() to Change Data Type

Below example cast’s selected columns using select() transformation. When you have many columns on DataFrame and wanted to cast selected columns this comes in handy.


val cast_df = df.select(df.columns.map {
    case [email protected]"age" =>
      col(column).cast("String").as(column)
    case [email protected]"salary" =>
      col(column).cast("String").as(column)
    case column =>
      col(column)
  }: _*)

cast_df.printSchema()

col(column).cast("String").as(column)) will be converted as CAST(YEAR AS STRING) AS YEAR. Yields below output.


root
 |-- firstName: string (nullable = true)
 |-- age: string (nullable = true)
 |-- jobStartDate: string (nullable = true)
 |-- isGraduated: string (nullable = true)
 |-- gender: string (nullable = true)
 |-- salary: string (nullable = true)

This example has been shared by @sriramrimmalapudi9gmail-com

3. Using selectExpr() to Change Data Type

Let’s use selectExpr() to convert spark DataFrame column age back to an integer, isGraduated from boolean to string and jobStartDate from date to String.


val df3 = df2.selectExpr("cast(age as int) age",
    "cast(isGraduated as string) isGraduated",
    "cast(jobStartDate as string) jobStartDate")
df3.printSchema()
df3.show(false)

root
 |-- age: integer (nullable = true)
 |-- isGraduated: string (nullable = true)
 |-- jobStartDate: string (nullable = true)

4. Using SQL Expression to Convert

We can also use SQL expression to change the spark DataFrame column type.


df3.createOrReplaceTempView("CastExample")
val df4 = spark.sql("SELECT STRING(age),BOOLEAN(isGraduated),
        DATE(jobStartDate) from CastExample")
df4.printSchema()
df4.show(false)

Outputs:


root
 |-- age: string (nullable = true)
 |-- isGraduated: boolean (nullable = true)
 |-- jobStartDate: date (nullable = true)

5. Complete Example of Casting DataFrame Column


package com.sparkbyexamples.spark.dataframe

import org.apache.spark.sql.{Row, SparkSession}
import org.apache.spark.sql.types._
import org.apache.spark.sql.functions._

object CastColumnType extends App{
  val spark: SparkSession = SparkSession.builder()
    .master("local[1]")
    .appName("SparkByExamples.com")
    .getOrCreate()

  val simpleData = Seq(Row("James",34,"2006-01-01","true","M",3000.60),
    Row("Michael",33,"1980-01-10","true","F",3300.80),
    Row("Robert",37,"06-01-1992","false","M",5000.50)
  )

  val simpleSchema = StructType(Array(
    StructField("firstName",StringType,true),
    StructField("age",IntegerType,true),
    StructField("jobStartDate",StringType,true),
    StructField("isGraduated", StringType, true),
    StructField("gender", StringType, true),
    StructField("salary", DoubleType, true)
  ))

  val df = spark.createDataFrame(
     spark.sparkContext.parallelize(simpleData),simpleSchema)
  df.printSchema()
  df.show(false)

  val df2 = df.withColumn("age",col("age").cast(StringType))
    .withColumn("isGraduated",col("isGraduated").cast(BooleanType))
    .withColumn("jobStartDate",col("jobStartDate").cast(DateType))
  df2.printSchema()

  val df3 = df2.selectExpr("cast(age as int) age",
    "cast(isGraduated as string) isGraduated",
    "cast(jobStartDate as string) jobStartDate")
  df3.printSchema()
  df3.show(false)

  df3.createOrReplaceTempView("CastExample")
  val df4 = spark.sql("SELECT STRING(age),BOOLEAN(isGraduated), " +
    "DATE(jobStartDate) from CastExample")
    df4.printSchema()
    df4.show(false)

  val cast_df = df.select(df.columns.map {
    case [email protected]"age" =>
      col(column).cast("String").as(column)
    case [email protected]"salary" =>
      col(column).cast("String").as(column)
    case column =>
      col(column)
  }: _*)

  cast_df.printSchema()
}

This example is also available at GitHub for reference.

Happy Learning !!

NNK

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This Post Has 6 Comments

  1. Navin

    I have use .selectExpr, it worked however this omits my other column in DF.

    1. NNK

      You should add all required columns into selectExpr(), This function results in a new DataFrame with just columns mentioned in it.

  2. Anonymous

    It always shows like name ‘NumericType’ is not defined, I don’t what I just missed from your article? I am so confused

    1. NNK

      Have you tried running complete example mentioned at the end of the post? just FYI, I’ve copied the code and tried it now and got the expected issue without any error. If you are still facing an error, please provide with a complete error stack trace.

    2. Emil

      You have not imported types – import org.apache.spark.sql.types._

      1. NNK

        Thanks Emil. I will add it.

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