def cols_to_slugify(df, columns):
    """Slugify selected column values and return dataframe.

    Args: 
        df: Pandas dataframe.
        columns: List of columns to convert.

    Returns: 
        Original dataframe with converted column data.
    """
    for col in columns:
        df[col] = df[col].str.replace('[^0-9a-zA-Z]+', '_', regex=True)
    return df
