code: def transform_expression_columns(df, fn=np.log2, prefix='Intensity '):
      
      df = df.copy()
  
      mask = np.array([l.startswith(prefix) for l in df.columns.values])
      df.iloc[:, mask] = fn(df.iloc[:, mask])
  
      df.replace([np.inf, -np.inf], np.nan, inplace=True)
      
      return df
docs: Apply transformation to expression columns.
  
      Default is log2 transform to expression columns beginning with Intensity
  
  
      :param df:
      :param prefix: The column prefix for expression columns
      :return: