class_docstr: Factorization Machines base class.
docstr: Infers feature field name.
docstr_tok: ["Infers","feature","field","name","."]
code: def _field(self, j):
      """Infers feature field name."""
      return j.split("_")[0]
  
imports: from __future__ import annotations
  import abc
  import collections
  import numbers
  from collections.abc import Iterable
  import numpy
  from river import optim, utils
label_desc: Use image node_id 7 for calling the BaseFM obj's underlying member method code with example usage: obj._field(j) and returns: j