Selecting 1st element of every list within list

Question

I have the following list of lists with multiple elements:

list = [[1633425661439, 0.11643042583898743],
        [1633428739018, 0.11682454707026001],
        [1633432086311, 0.11950356856187618]]

I want to populate a new_list1 and new_list2 with the first and second numbers within each of those lists, respectively, yielding:

new_list1 = [1633425661439,
            1633428739018,
            1633432086311]

And:

new_list2 = [0.11643042583898743,
            0.11682454707026001,
            0.11950356856187618]

I tried:

for n in list:
        for i in n:
            new_list1.append(i[0])
            new_list2.append(i[1])

But got: TypeError: 'int' object is not subscriptable

Answer 1

You can transpose it like this:

lst = [[1633425661439, 0.11643042583898743],
       [1633428739018, 0.11682454707026001],
       [1633432086311, 0.11950356856187618]]

new_list_1, new_list_2 = map(list, zip(*lst))

And if you are ok with tuples instead of lists, the following will do:

new_list_1, new_list_2 = zip(*lst)

And you really should not name a variable list . It shadows the built-in type.

You can also use simple comprehensions:

new_list_1 = [a for a, _ in lst]
new_list_2 = [a for _, a in lst]

Some docs:

• map
• zip

Answer 2

You can try something

list_ = [[1633425661439, 0.11643042583898743],
        [1633428739018, 0.11682454707026001],
        [1633432086311, 0.11950356856187618]]

list_a = [first[0] for first in list_]
list_b = [first[1] for first in list_]

Other way

new_list1 = []
new_list2 = []

for inner_list in list_:
    new_list1.append(inner_list[0])
    new_list2.append(inner_list[1])

Answer 3

You have one level of nesting too much, this would

for n in list:
    for i in n:
        print(i)

would print single elements, which are numbers, you need to do

for n in list:
    new_list1.append(n[0])
    new_list2.append(n[1])

As side note, please avoid using list as it is already used name in python . Overshadowing it might cause unexpected behavior, you can use lst name ie:

lst = [[1,2],[3,4],[5,6]]
new_lst1 = []
new_lst2 = []
for n in lst:
    new_lst1.append(n[0])
    new_lst2.append(n[1])
print(new_lst1)
print(new_lst2)

output

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

Answer 4

you can unpack the first and second number in the for loop itself. (BTW best not call the variable "list" because it is the same as a python build-in)

list_ = [[1633425661439, 0.11643042583898743],
        [1633428739018, 0.11682454707026001],
        [1633432086311, 0.11950356856187618]]
new_list1 = []
new_list2 = []
for (i, j) in l:
    new_list1.append(i)
    new_list2.append(j)

Answer 5

1. Following PEP-8 code style guideline please do not name the variables with reserved keywords like list , dict , for , etc.

2. With the second loop you iterate over int numbers within the inner lists. If you need to use only the first 2 elements of each list, one loop os enough:

list_ = [
    [1633425661439, 0.11643042583898743],
    [1633428739018, 0.11682454707026001],
    [1633432086311, 0.11950356856187618]]

for inner_list in list_:
    new_list1.append(inner_list[0])
    new_list2.append(inner_list[1])
    

Answer 6

list= [[1633425661439, 0.11643042583898743], [1633428739018, 0.11682454707026001], [1633432086311, 0.11950356856187618]]
new_list1 = [ ] 
new_list2 = [ ] 
for inner_list in list:
   new_list1.append(inner_list[0])
   new_list2.append(inner_list[1])
print(new_list1)
print(new_list2)