def select_data(nwis_df):
    """Create a boolean array of columns that contain data.

    Args:
        nwis_df:
            A pandas dataframe created by ``extract_nwis_df``.

    Returns:
        an array of Boolean values corresponding to the columns in the
        original dataframe.

    Example:

        >>> my_dataframe[:, select_data(my_dataframe)]

        returns a dataframe with only the data columns; the qualifier columns
        do not show.
    """
    data_regex = r"[0-9]$"
    return nwis_df.columns.str.contains(data_regex)