How to add header and column to dataframe spark? - scala

Question

I have got a dataframe, on which I want to add a header and a first column
manually. Here is the dataframe :
import org.apache.spark.sql.SparkSession
val spark = SparkSession.builder.master("local").appName("my-spark-app").getOrCreate()
val df = spark.read.option("header",true).option("inferSchema",true).csv("C:\\gg.csv").cache()
the content of the dataframe
12,13,14
11,10,5
3,2,45
The expected output is
define,col1,col2,col3
c1,12,13,14
c2,11,10,5
c3,3,2,45

Answer 1

What you want to do is:
df.withColumn("columnName", column) //here "columnName" should be "define" for you
Now you just need to create the said column (this might help)

Answer 2

Here is a solution that depends on Spark 2.4:
import org.apache.spark.sql.SparkSession
import org.apache.spark.sql.types.{IntegerType, StringType, StructField, StructType}
import org.apache.spark.sql.Row
//First off the dataframe needs to be loaded with the expected schema
val spark = SparkSession.builder().appName().getOrCreate()
val schema = new StructType()
.add("col1",IntegerType,true)
.add("col2",IntegerType,true)
.add("col3",IntegerType,true)
val df = spark.read.format("csv").schema(schema).load("C:\\gg.csv").cache()
val rddWithId = df.rdd.zipWithIndex
// Prepend "define" column of type Long
val newSchema = StructType(Array(StructField("define", StringType, false)) ++ df.schema.fields)
val dfZippedWithId = spark.createDataFrame(rddWithId.map{
case (row, index) =>
Row.fromSeq(Array("c" + index) ++ row.toSeq)}, newSchema)
// Show results
dfZippedWithId.show
Displays:
+------+----+----+----+
|define|col1|col2|col3|
+------+----+----+----+
| c0| 12| 13| 14|
| c1| 11| 10| 5|
| c2| 3| 2| 45|
+------+----+----+----+
This is a mix of the documentation here and this example.