Let's say I have the following main_list that contains other small_lists:
main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]]
I want to find the small_list knowing the index 0 and 1 of the small_lists. So for instance, how can I create a getlist() function such that:
getlist(4,5) = [4, 5, 6, 7]
getlist(0,1) = [0, 1, 2, 3]
getlist(5,5) = None
getlist(9,10) = None
The simplest way is to map your list to a dictionary, where the keys are set to what you wan't to retrieve by. This can be done quickly using list comprehension as per the example below.
>>> main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]]
>>> indexed_list = { (i[0], i[1]) : i for i in main_list }
>>> indexed_list.get( (0,1) )
[0, 1, 2, 3]
>>> indexed_list.get( (4,5) )
[4, 5, 6, 7]
>>> indexed_list.get( (5,5) )
None
The code below should solve your problem, or at least get you on the right track. It is also available here on OnlineGDB for further tinkering, if you need.
main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]]
def getlist(idx0, idx1):
# Assumes there isn't a match, unless one is found
target_list = None
# Loops through the list of lists, checking for a match with the characters at index 0 and 1
for sub_list in main_list:
if idx0 == sub_list[0] and idx1 == sub_list[1]:
target_list = sub_list
# returns the target list (if it found) or None (if it isn't)
return target_list
print(getlist(4,5))
>>[4, 5, 6, 7]
print(getlist(0,1))
>>[0, 1, 2, 3]
print(getlist(5,5))
>>None
print(getlist(9,10))
>>None
Checking sliced list would work here, This also works if there are more than one matching list with starting indexes similar to argument.
>>> main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]]
>>> def get_list(tup, list_group):
... return [list_ for list_ in list_group if list_[:2] == list(tup)]
...
>>> print(get_list((0, 1), main_list))
[[0, 1, 2, 3]]
>>> main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [0, 1, 10, 7]] # multiple occurence
>>> print(get_list((0, 1), main_list))
[[0, 1, 2, 3], [0, 1, 10, 7]]
That's a weird way of classifying your elements. There are more suitable way's of storing your data lice dictionaries.
main_list = [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]]
def getlist(a,b):
for sub_list in main_list:
if [a,b] == sub_list[0:2]:
return sub_list
>>> print (getlist(4,5))
>>> print (getlist(2,1))
[4, 5, 6, 7]
None
sub_list