class_docstr: Mixin for user-defined rolling-window Terms.
  
  Implements `_compute` in terms of a user-defined `compute` function, which
  is mapped over the input windows.
  
  Used by CustomFactor, CustomFilter, CustomClassifier, etc.
code: def _format_inputs(self, windows, column_mask):
      inputs = []
      for input_ in windows:
          window = next(input_)
          if window.shape[1] == 1:
              # Do not mask single-column inputs.
              inputs.append(window)
          else:
              inputs.append(window[:, column_mask])
      return inputs
  
imports: from textwrap import dedent
  from numpy import array, full, recarray, vstack
  from pandas import NaT
  from catalyst.errors import WindowLengthNotPositive, UnsupportedDataType, NoFurtherDataError
  from catalyst.utils.control_flow import nullctx
  from catalyst.utils.input_validation import expect_types
  from catalyst.utils.sharedoc import format_docstring, PIPELINE_ALIAS_NAME_DOC, PIPELINE_DOWNSAMPLING_FREQUENCY_DOC
  from catalyst.utils.pandas_utils import nearest_unequal_elements
  from .downsample_helpers import select_sampling_indices, expect_downsample_frequency
  from .sentinels import NotSpecified
  from .term import Term
label_desc: Use image node_id 4 for calling the CustomTermMixin obj's underlying member method code with example usage: obj._format_inputs(windows, column_mask) and returns: inputs