how to cast all columns of dataframe to string

Question

I have a mixed type dataframe. I am reading this dataframe from hive table using spark.sql('select a,b,c from table') command.

Some columns are int , bigint , double and others are string. There are 32 columns in total. Is there any way in pyspark to convert all columns in the data frame to string type ?

Answer 1

Just:

from pyspark.sql.functions import col

table = spark.sql("table")

table.select([col(c).cast("string") for c in table.columns])

Answer 2

Here's a one line solution in Scala :

df.select(df.columns.map(c => col(c).cast(StringType)) : _*)

Let's see an example here :

import org.apache.spark.sql._
import org.apache.spark.sql.types._
import org.apache.spark.sql.functions._
val data = Seq(
   Row(1, "a"),
   Row(5, "z")
)

val schema = StructType(
  List(
    StructField("num", IntegerType, true),
    StructField("letter", StringType, true)
 )
)

val df = spark.createDataFrame(
  spark.sparkContext.parallelize(data),
  schema
)

df.printSchema
//root
//|-- num: integer (nullable = true)
//|-- letter: string (nullable = true)

val newDf = df.select(df.columns.map(c => col(c).cast(StringType)) : _*)

newDf.printSchema
//root
//|-- num: string (nullable = true)
//|-- letter: string (nullable = true)

I hope it helps