iterating through a list to append a value to variable lists

Question

I have the following data:

data = [['AB', 'BS, BT'], ['AH', 'AH'], ['AS', 'AS, GS']]

I would like to iterate through the lists of list to produce a list of tuples.

new_data = [('AB', 'BS'), ('AB', 'BT'), ('AH', 'AH'), ('AS', 'AS') ('AS', 'GS')]

I was thinking about using the zip() function, but wasn't sure if I was using the right logic.

Answer 1

zip wouldn't be my first choice. My first choice would be itertools.product and itertools.chain

In [103]: data = [['AB', 'BS, BT'], ['AH', 'AH'], ['AS', 'AS, GS']]

In [104]: [list(itertools.product([d[0]], d[1].split(','))) for d in data]
Out[104]: [[('AB', 'BS'), ('AB', ' BT')], [('AH', 'AH')], [('AS', 'AS'), ('AS', ' GS')]]

In [105]: list(itertools.chain.from_iterable([list(itertools.product([d[0]], d[1].split(','))) for d in data]))
Out[105]: [('AB', 'BS'), ('AB', ' BT'), ('AH', 'AH'), ('AS', 'AS'), ('AS', ' GS')]

Hope this helps

Answer 2

This can be done easily enough with itertools.repeat() . We use this to repeat the first item for each of the other items, which we get by splitting on "," , then zipping up to generate our tuples. We then use itertools.chain.from_iterable() to generate a single list.

>>> import itertools
>>> data = [['AB', 'BS, BT'], ['AH', 'AH'], ['AS', 'AS, GS']]
>>> for item in itertools.chain.from_iterable(zip(itertools.repeat(first), second.split(",")) for first, second in data):
...     print(item)
... 
('AB', 'BS')
('AB', ' BT')
('AH', 'AH')
('AS', 'AS')
('AS', ' GS')

Answer 3

using zip() :

In [32]: data
Out[32]: [['AB', 'BS, BT'], ['AH', 'AH'], ['AS', 'AS, GS']]

In [33]: [zip([x[0]]*len(x[1].split(",")),x[1].split(",")) for x in data]
Out[33]: [[('AB', 'BS'), ('AB', ' BT')], [('AH', 'AH')], [('AS', 'AS'), ('AS', ' GS')]]

use chain() to get the expected output:

In [34]: lis=[zip([x[0]]*len(x[1].split(",")),x[1].split(",")) for x in data]

In [35]: list(chain(*lis))
Out[35]: [('AB', 'BS'), ('AB', ' BT'), ('AH', 'AH'), ('AS', 'AS'), ('AS', ' GS')]

using izip_longest , with fillvalue equal to first element of each sublist:

In [47]: from itertools import chain,izip_longest

In [48]: lis=[tuple(izip_longest([x[0]],x[1].split(","),fillvalue=x[0])) for x in data]

In [49]: lis
Out[49]: [(('AB', 'BS'), ('AB', ' BT')), (('AH', 'AH'),), (('AS', 'AS'), ('AS', ' GS'))]

In [50]: list(chain(*lis))
Out[50]: [('AB', 'BS'), ('AB', ' BT'), ('AH', 'AH'), ('AS', 'AS'), ('AS', ' GS')]