The CDK Fingerprint Similarity node has an undocumented feature when searching for the Max or Min Tanimoto similarity in that it returns a "Reference" column with the RowIDs which correspond to that Max or Min Similarity. This is a nice feature which other Fingerprint Similarity nodes in KNIME do not have, so it may be useful capturing this in the node dialog box.
I have noticed for Similarity ties, it separates the RowIDs with a | character. It may be more useful to have the "Reference" column as a Collection Type column so that the user can manipulate the list of RowIDs better (i.e. using UnGroup node or Split Collection Column node).
If I dare mention the java snippet (the old 'simple' one!), then setting the return type to string and checking the 'array return' box, and use the snippet
return $Reference$.split("|");
will have the desired effect in the interim (although I agree that the option to return as a set/collection might be useful)
now it is documented. :) Thanks for pointing that out.
I agree that it would be useful to offer the option to return a collection type cell, even though the Java snippet is still one useful node! I have altered the node to that effect.