Merging list elements into one list of dataframe in Pandas

Question

I have a dataframe read from csv file, it similar to the following:

                    LIST-1  LIST-2        LIST-3              ... LIST-N
TIME                                           
2017-06-21 00:17:00 NaN     [99.221]       [42.357, 102.665]
2017-06-21 00:18:00 NaN     [50.89]        [42.357, 43.125,...]
2017-06-21 00:19:00 NaN     [61.50, 76.1]  [70.163, 121.486] 
2017-06-21 00:20:00 [70.16] NaN            NaN
2017-06-21 00:21:00 NaN     [102.665]      [57.9, 63.66, 68.7... 

Each line represents one minute of data, the dtype of list_N column is object. I want to do the ：

1. Merge all the lists in each row into a float list and use the list as a new column-- ALL_LIST ;
2. Then, merge the thirty minutes of data（ (that is, thirty rows of data-- ALL_LIST ) ） into a new list;

3. Finally, I want to get a dataframe like this:

   \nTIME LIST                                          \n2017-06-21 00:00:00 [99.221，42.357, 42.357, ...] \n2017-06-21 00:30:00 [52.328，42.357, 49.169， ...] \n2017-06-21 01:00:00 [61.484，42.357, 76.52， ...] \n2017-06-21 01:30:00 [76.523，42.357, 121.486， ...] \n

Answer 1

I found one solution for my question. I'll write it out and hope to see whether it can improve performance.

    all_tt_list['ALL_LIST'] = all_tt_list.apply(lambda x: ','.join(x.dropna()), axis=1)
    all_tt_list['ALL_LIST'] = all_tt_list['ALL_LIST'].astype(str).str.replace('[', '')
    all_tt_list['ALL_LIST'] = all_tt_list['ALL_LIST'].astype(str).str.replace(']', '')
    all_tt_list['ALL_LIST'] = all_tt_list['ALL_LIST'].astype(str).str.split(',')
    WAIT_TIME_INTERVAL = 30*60
    rng = pd.date_range(date, periods=(24 * 60 * 60 / WAIT_TIME_INTERVAL) + 1, freq=str(WAIT_TIME_INTERVAL) + 'S',
                    tz='Asia/Shanghai')
    for k in range(len(rng)):

        if(k == (len(rng)-1)):
            continue

        period_start = rng[k]
        period_end = rng[k+1]
        period_df = all_tt_list[all_tt_list.index > period_start]
        period_df = period_df[period_df.index < period_end]

        period_tt_list = period_df['ALL_LIST'].tolist()
        import itertools

        period_merged = list(itertools.chain.from_iterable(period_tt_list))

        period_merged_s = pd.DataFrame(period_merged, columns=['TT_NUM']).astype(float).astype(int)