Grouping Lists in Python

Question

I am trying to group many lists together based on a common index. The common index is a Julian Date (JD) and I would like to merge all the other times in other lists that share the same JD to a single list containing the single JD and all respective times. However, I keep getting a "TypeError: list indices must be integers, not tuple" and I am not sure why this occurring. Am I not originally assigning the variable "list_of_lsts" an actual list of lists or am I messing up somewhere in my loop. My end result would be the following:

['2014-158', '20:07:11.881', '20:43:04.546', '20:43:47.447', '21:11:08.997', '21:11:16.697', '21:22:07.717']
['2014-163', '17:12:09.071', '17:38:08.219', '17:38:28.310', '17:59:25.649','18:05:59.536', '18:09:53.243','18:13:47.671', '18:16:53.976', '18:20:31.538', '18:23:02.243']

I will be doing this for many Julian dates so the loop is necessary. I am a new programmer and most of all new to Python 2.7.8 so please forgive the ignorance and copious mistakes. Thank you.

lst_of_lsts = (['2014-158', '20:07:11.881', '20:43:04.546']
               ['2014-158', '20:43:47.447', '21:11:08.997']
               ['2014-158', '21:11:16.697', '21:22:07.717']
               ['2014-163', '17:12:09.071', '17:38:08.219']
               ['2014-163', '17:38:28.310', '17:59:25.649']
               ['2014-163', '18:05:59.536', '18:09:53.243']
               ['2014-163', '18:13:47.671', '18:16:53.976']
               ['2014-163', '18:20:31.538', '18:23:02.243'])


def merge_subs(lst_of_lsts):
    res = []
    for row in lst_of_lsts:
        for i, resrow in enumerate(res):
            if row[0]==resrow[0]:
                res[i] += row[1:]
                break
            else:
                res.append(row)
        return res

Answer 1

Change to

lst_of_lsts = (['2014-158', '20:07:11.881', '20:43:04.546'],
['2014-158', '20:43:47.447', '21:11:08.997'],
['2014-158', '21:11:16.697', '21:22:07.717'],
['2014-163', '17:12:09.071', '17:38:08.219'],
['2014-163', '17:38:28.310', '17:59:25.649'],
['2014-163', '18:05:59.536', '18:09:53.243'],
['2014-163', '18:13:47.671', '18:16:53.976'],
['2014-163', '18:20:31.538', '18:23:02.243'])

That is, you're missing commas.

Another change I would suggest:

for i, resrow in enumerate(res):
        if row[0]==resrow[0]:
            res[i] += row[1:]

Here res[i] and resrow are the same things - as in a change to one will change the other. No need to have both of them. Instead do

for resrow in res:
    if row[0] == resrow[0]:
        resrow += row[1:]

Also - as currently indented the else will not be done if the if fails. Rather, it'll be done after the for loop. I don't think that is what you intend.

Really though, you want to use a dict.

def merge_subs2(lst_of_lsts):
    date_dict = {}
    for row in lst_of_lsts:
        if row[0] not in date_dict:
            date_dict[row[0]] = [row[0]] #note that I'm putting row[0] here already.
        date_dict[row[0]].extend(row[1:])
    returnlist = date_dict.values()
    returnlist.sort()   #sorting because dicts don't have an order to them.
    return returnlist

Answer 2

def merge_subs(L):
    dates = {}
    for sub in L:
        date = sub[0]
        if date not in dates:
            dates[date] = []
        dates[date].extend(sub[1:])
    answer = []
    for date in sorted(dates):
        answer.append([date] + dates[date])
    return answer

Output:

In [28]: lst_of_lsts = (['2014-158', '20:07:11.881', '20:43:04.546'],
['2014-158', '20:43:47.447', '21:11:08.997'],
['2014-158', '21:11:16.697', '21:22:07.717'],
['2014-163', '17:12:09.071', '17:38:08.219'],
['2014-163', '17:38:28.310', '17:59:25.649'],
['2014-163', '18:05:59.536', '18:09:53.243'],
['2014-163', '18:13:47.671', '18:16:53.976'],
['2014-163', '18:20:31.538', '18:23:02.243'])

In [29]: merge_subs(lst_of_lsts)
Out[29]: [['2014-158', '20:07:11.881', '20:43:04.546', '20:43:47.447', '21:11:08.997', '21:11:16.697', '21:22:07.717'], 
          ['2014-163', '17:12:09.071', '17:38:08.219', '17:38:28.310', '17:59:25.649', '18:05:59.536', '18:09:53.243', '18:13:47.671', '18:16:53.976', '18:20:31.538', '18:23:02.243']]