How to add 'other' as one group to clustering algorithm inference pipeline
Clustering doesn't work like this: for example k-means assigns an instance to the closest centroid, and since there is always a closest centroid there is a always a cluster that an instance &quot;belongs to&quot;.
So you need a different approach if you plan to have the possibility of in instance &quot;not in any group&quot;:

redo the clustering on the full set of instances
apply a first step which detects outliers
train a one-class classification model for every cluster