ConcatWith and AsVector need to be more restrictive regarding types they can be applicable.

[Ivanidzo4ka]

var pipe = data.MakeNewEstimator().Append(row => (label: row.label.ToKey(), features: row.image.LoadAsImage()));

I'm loading images. As soon as I hit dot after LoadAsImage I get suggestions to Resize and AsGreyscale
which make sense. But I also got suggestion from intellisence to apply AsVector and ConcatWith. Which doesn't make much sense for me.

[TomFinley]

Hmmm. Perhaps Scalar<> and Vector<> and the like should be reserved for primitive types, and there should be another subclass out of PipelineColumn for non-vector structural types.