code: def _format_x(self, x):
      return " ".join(f"{k}:{v}" for k, v in x.items())
  
file_path: river/benchmarks/model_adapters/vw.py
imports: from __future__ import annotations
  from vowpalwabbit import pyvw
  from river import base
label_desc: Use image node_id 2 for calling the VW2RiverBase obj's underlying member method code with example usage: obj._format_x(x) and returns: str