how to cast all columns of dataframe to string - apache-spark

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

Answer 3

for col in df_data.columns:
df_data = df_data.withColumn(col, df_data[col].cast(StringType()))

Answer 4

For Scala, spark version > 2.0
case class Row(id: Int, value: Double)
import spark.implicits._
import org.apache.spark.sql.functions._
val r1 = Seq(Row(1, 1.0), Row(2, 2.0), Row(3, 3.0)).toDF()
r1.show
+---+-----+
| id|value|
+---+-----+
| 1| 1.0|
| 2| 2.0|
| 3| 3.0|
+---+-----+
val castedDF = r1.columns.foldLeft(r1)((current, c) => current.withColumn(c, col(c).cast("String")))
castedDF.printSchema
root
|-- id: string (nullable = false)
|-- value: string (nullable = false)

Answer 5

you can cast single column as this
import pyspark.sql.functions as F
import pyspark.sql.types as T
df = df.withColumn("id", F.col("new_id").cast(T.StringType()))
and just for all column to cast