MatchError while accessing vector column in Spark 2.0

This has nothing to do with sparsity. Since Spark 2.0.0 ML Transformers no longer generate o.a.s.mllib.linalg.VectorUDT but o.a.s.ml.linalg.VectorUDT and are mapped locally to subclasses of o.a.s.ml.linalg.Vector. These are not compatible with old MLLib API which is moving towards deprecation in Spark 2.0.0.

You can convert between to “old” using Vectors.fromML:

import org.apache.spark.mllib.linalg.{Vectors => OldVectors}
import org.apache.spark.ml.linalg.{Vectors => NewVectors}

OldVectors.fromML(NewVectors.dense(1.0, 2.0, 3.0))
OldVectors.fromML(NewVectors.sparse(5, Seq(0 -> 1.0, 2 -> 2.0, 4 -> 3.0)))

but it make more sense to use ML implementation of LDA if you already use ML transformers.

For convenience you can use implicit conversions:

import scala.languageFeature.implicitConversions

object VectorConversions {
  import org.apache.spark.mllib.{linalg => mllib}
  import org.apache.spark.ml.{linalg => ml}

  implicit def toNewVector(v: mllib.Vector) = v.asML
  implicit def toOldVector(v: ml.Vector) = mllib.Vectors.fromML(v)
}

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