append 如果满足条件，则另一个嵌套列表中的嵌套列表的最后一个元素

Question

I have 2 list of lists:

a = [[1,2,3], [4,5,6]]
b= [[1,8,9], [4,10,11]]

I want to add the last elements in any list of b to the end of list a if they share the first element.

for example, in my above lists, a and b share the first elements in their nested lists

a[0][0] = b[0][0]
a[1][0] = b[1][0]

the result I want is

a = [[1,2,3,9], [4,5,6,11]]

Answer 1

If you know that a & b lists have the same length you can do it like this:

a = [[1,2,3], [4,5,6]]
b = [[1,8,9], [4,10,11]]

for x in range(len(a)):
    if a[x][0] == b[x][0]:
        a[x].append(b[x][-1])
print(a)

Answer 2

for item_a, item_b in zip(a,b):
    if item_a[0] == item_b[0]:
        item_a.append(item_b[-1])

Answer 3

Using zip to combine combine a,b by index. List comprehension to append B[-1] if first element matches.

print([A+B[-1:] if A[0]==B[0] else A for A,B in zip(a,b)])

Answer 4

If you don't know the size of the lists then:

def main(input_list1, input_list2):
    return_list = []
    for combined_lists in zip(input_list1, input_list2):
        list1 = combined_lists[0]
        list2 = combined_lists[1]
        first_idx1 = list1[0]
        first_idx2 = list2[0]
        if first_idx1 == first_idx2:
            last_index2 = list2[len(list2)-1]
            current_list = []
            for elem in list1:
                current_list.append(elem)
            current_list.append(last_index2)
            return_list.append(current_list)
    return return_list


if __name__ == '__main__':
    a = [[1, 2, 3], [4, 5, 6]]
    b = [[1, 8, 9], [4, 10, 11]]
    ret_list = main(input_list1=a, input_list2=b)
    print(ret_list)

Output is:

[[1, 2, 3, 9], [4, 5, 6, 11]]