def validate_multiple_cols(clsname, cols):
    """Validate that there are at least two columns to evaluate.

    This is used for various feature selection techniques, as well as
    in several feature extraction techniques.

    Parameters
    ----------
    clsname : str or unicode
        The name of the class that is calling the function.
        Used for more clear error messages.

    cols : array-like, shape=(n_features,)
        The columns to evaluate. If ``cols`` is not None
        and the length is less than 2, will raise a
        ``ValueError``.
    """
    if len(cols) < 2:
        raise ValueError(
            '%s requires at least two features. Your data (or the passed ``cols`` parameter) includes too few features (%i)'
             % (clsname, len(cols)))
