I have a sample Dataframe that I create using below code
val data = Seq(
Row(20.0, "dog"),
Row(3.5, "cat"),
Row(0.000006, "ant")
)
val schema = StructType(
List(
StructField("weight", DoubleType, true),
StructField("animal_type", StringType, true)
)
)
val df = spark.createDataFrame(
spark.sparkContext.parallelize(data),
schema
)
val actualDF = df.withColumn(
"animal_interpretation",
struct(
(col("weight") > 5).as("is_large_animal"),
col("animal_type").isin("rat", "cat", "dog").as("is_mammal")
)
)
actualDF.show(false)
+------+-----------+---------------------+
|weight|animal_type|animal_interpretation|
+------+-----------+---------------------+
|20.0 |dog |[true,true] |
|3.5 |cat |[false,true] |
|6.0E-6|ant |[false,false] |
+------+-----------+---------------------+
The schema of this Spark DF can be printed using -
scala> actualDF.printSchema
root
|-- weight: double (nullable = true)
|-- animal_type: string (nullable = true)
|-- animal_interpretation: struct (nullable = false)
| |-- is_large_animal: boolean (nullable = true)
| |-- is_mammal: boolean (nullable = true)
However, I would like to get this schema in the form of a dataframe that has 3 columns - field, type, nullable
. The output dataframe from the schema would something like this -
+-------------------------------------+--------------+--------+
|field |type |nullable|
+-------------------------------------+--------------+--------+
|weight |double |true |
|animal_type |string |true |
|animal_interpretation |struct |false |
|animal_interpretation.is_large_animal|boolean |true |
|animal_interpretation.is_mammal |boolean |true |
+----------------------------------------------------+--------+
How can I achieve this in Spark. I am using Scala for coding.
You could do something like this
def flattenSchema(schema: StructType, prefix: String = null) : Seq[(String, String, Boolean)] = {
schema.fields.flatMap(field => {
val col = if (prefix == null) field.name else (prefix + "." + field.name)
field.dataType match {
case st: StructType => flattenSchema(st, col)
case _ => Array((col, field.dataType.simpleString, field.nullable))
}
})
}
flattenSchema(actualDF.schema).toDF("field", "type", "nullable").show()
Hope this helps!
Here is a complete example including your code. I used the somewhat common flattenSchema method for matching like Shankar did to traverse the Struct but rather than having this method return the flattened schema I used an ArrayBuffer to aggregate the datatypes of the StructType and returned the ArrayBuffer. I then turned the ArrayBuffer into a Sequence and finally, using Spark, converted the Sequence to a DataFrame.
import org.apache.spark.sql.types.{StructType, StructField, DoubleType, StringType}
import org.apache.spark.sql.functions.{struct, col}
import scala.collection.mutable.ArrayBuffer
val data = Seq(
Row(20.0, "dog"),
Row(3.5, "cat"),
Row(0.000006, "ant")
)
val schema = StructType(
List(
StructField("weight", DoubleType, true),
StructField("animal_type", StringType, true)
)
)
val df = spark.createDataFrame(
spark.sparkContext.parallelize(data),
schema
)
val actualDF = df.withColumn(
"animal_interpretation",
struct(
(col("weight") > 5).as("is_large_animal"),
col("animal_type").isin("rat", "cat", "dog").as("is_mammal")
)
)
var fieldStructs = new ArrayBuffer[(String, String, Boolean)]()
def flattenSchema(schema: StructType, fieldStructs: ArrayBuffer[(String, String, Boolean)], prefix: String = null): ArrayBuffer[(String, String, Boolean)] = {
schema.fields.foreach(field => {
val col = if (prefix == null) field.name else (prefix + "." + field.name)
field.dataType match {
case st: StructType => {
fieldStructs += ((col, field.dataType.typeName, field.nullable))
flattenSchema(st, fieldStructs, col)
}
case _ => {
fieldStructs += ((col, field.dataType.simpleString, field.nullable))
}
}}
)
fieldStructs
}
val foo = flattenSchema(actualDF.schema, fieldStructs).toSeq.toDF("field", "type", "nullable")
foo.show(false)
If you run the above you should get the following.
+-------------------------------------+-------+--------+
|field |type |nullable|
+-------------------------------------+-------+--------+
|weight |double |true |
|animal_type |string |true |
|animal_interpretation |struct |false |
|animal_interpretation.is_large_animal|boolean|true |
|animal_interpretation.is_mammal |boolean|true |
+-------------------------------------+-------+--------+
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