Get Column Names after columnSimilarties() Spark scala

Question

I'm trying to build item based collaborative filtering model with columnSimilarities() in spark. After using the columnsSimilarities() I want to assign the original column names back to the results in Spark scala.

Runnable code to calculate columnSimilarities() on data frame.

Data

// rdd
val rowsRdd: RDD[Row] = sc.parallelize(
  Seq(
    Row(2.0, 7.0, 1.0),
    Row(3.5, 2.5, 0.0),
    Row(7.0, 5.9, 0.0)
  )
)

// Schema  
val schema = new StructType()
  .add(StructField("item_1", DoubleType, true))
  .add(StructField("item_2", DoubleType, true))
  .add(StructField("item_3", DoubleType, true))

// Data frame  
val df = spark.createDataFrame(rowsRdd, schema) 

Calculate columnSimilarities() on that data frame:

import org.apache.spark.ml.feature.VectorAssembler
import org.apache.spark.mllib.linalg.distributed.{MatrixEntry, CoordinateMatrix, RowMatrix}

val rows = new VectorAssembler().setInputCols(df.columns).setOutputCol("vs")
  .transform(df)
  .select("vs")
  .rdd

val items_mllib_vector = rows.map(_.getAs[org.apache.spark.ml.linalg.Vector](0))
                             .map(org.apache.spark.mllib.linalg.Vectors.fromML)
val mat = new RowMatrix(items_mllib_vector)
val simsPerfect = mat.columnSimilarities()


simsPerfect.entries.collect.mkString(", ")

Output:

res0: String = MatrixEntry(0,2,0.24759378423606918), MatrixEntry(1,2,0.7376189553526812), MatrixEntry(0,1,0.8355316482961213)

I've to get the original names from columns instead of the position in that vector.

I tried to read the column names from df with:

val names = df.columns

and my idea was to match the names with the positions in that vector wich should be in the same order, but I don't know how to attach the names back into that vector with the cosineSimilarities.

I'm happy for any advice!!

Answer 1

Extract columns names (this is the tricky part here because it cannot be evaluated in the closure):

val names = df.columns

and map the entries:

simsPerfect.entries.map {
  case MatrixEntry(i, j, v)  => (names(i.toInt),  names(j.toInt), v)
}