def FE_concatenate_multiple_columns(df, cols, filler=" ", drop=True):
    """
    This handy function combines multiple string columns into a single NLP text column.
    You can do further pre-processing on such a combined column with TFIDF or BERT style embedding.

    Inputs
    ---------
        df: pandas dataframe
        cols: string columns that you want to concatenate into a single combined column
        filler: string (default: " "): you can input any string that you want to combine them with.
        drop: default True. If True, drop the columns input. If False, keep the columns.

    Outputs:
    ----------
        df: there will be a new column called ['combined'] that will be added to your dataframe.
    """
    df = df.copy(deep=True)
    df['combined'] = df[cols].apply(lambda row: filler.join(row.values.astype(str)), axis=1)
    if drop:
        df = df.drop(cols, axis=1)
    return df