class_docstr: Shared set-up checks and methods across selectors.
  
  Parameters
  ----------
  confirm_variables: bool, default=False
      If set to True, variables that are not present in the input dataframe will be
      removed from the indicated list of variables. See parameter variables for more
      details.
  
  Methods
  -------
  transform:
      Remove non-selected features.
  
  _confirm_variables:
      Check that the variables entered by the user exist in the df.
class_docstr_tok: ["Shared","set-up","checks","and","methods","across","selectors",".","Parameters","--","--","--","--","--","confirm_variables",":","bool",",","default=False","If","set","to","True",",","variables","that","are","not","present","in","the","input","dataframe","will","be","removed","from","the","indicated","list","of","variables",".","See","parameter","variables","for","more","details",".","Methods","--","--","--","-","transform",":","Remove","non-selected","features",".","_confirm_variables",":","Check","that","the","variables","entered","by","the","user","exist","in","the","df","."]
docstr: Check that there are multiple variables for the selectors to work with.
docstr_tok: ["Check","that","there","are","multiple","variables","for","the","selectors","to","work","with","."]
code: def _check_variable_number(self) -> None:
      """Check that there are multiple variables for the selectors to work with."""
      if len(self.variables_) < 2:
          raise ValueError(
              "The selector needs at least 2 or more variables to select from. "
              f"Got only 1 variable: {self.variables_}."
          )
  
imports: import numpy
  import pandas
  from sklearn.base import BaseEstimator, TransformerMixin
  from sklearn.utils.validation import check_is_fitted
  from feature_engine._base_transformers.mixins import GetFeatureNamesOutMixin
  from feature_engine._variable_handling.variable_type_selection import _filter_out_variables_not_in_dataframe
  from feature_engine.dataframe_checks import _check_X_matches_training_df, check_X
  from feature_engine.tags import _return_tags
label_desc: Use image node_id 5 for calling the BaseSelector obj's underlying member method code with example usage: obj._check_variable_number() without return types