Double dispatch for #fit: method

[hernanmd]

Currently I'm using k-means with DataFrame as follows:

| df kmeans |
df := Datasets loadIris columnsFrom: 1 to: 4.
kmeans := KMeans numberOfClusters: 3.
kmeans fit: (df asArrayOfRows collect: #asArray).

It would be nice if the argument to #fit: could be just the DataFrame, which knows how to be fitted with a KMeans algorithm:

kmeans fit: df

This way fit could receive also PMMatrix and similar matrix-like objects. And each one is responsible to implement:

DataFrame>>fitKMeans: aKmeans
  aKmeans fit: (self asArrayOfRows collect: #asArray).

and so on...

[jordanmontt]

Yes, this is an issue for all the ml algos that we have. We should make them compatible with DataFrame