python条件访问列表列表

Question

I would like some suggestion on a problem concerning the access of data stored in a list of lists.

My list of lists looks like this:

my_list = [['RN1', 200, 0.55], ['RN2', 0.8, 0.44], ['RN3', 0.2, 0.01]]

The list is ordered with respect of the third element of the inner lists.

What I want to do is:

1. To check if the third element of the first inner list is greater or equal to 0.9; if yes, i want to create a list containing the first 2 elements of the first inner list

    my_list[0][2] >= 0.9 

   Which if true would give:

    new_list = [['RN1', 200]] 

2. If not, I want to add to my_list[0][2] element the corresponding element of the second inner list:

   my_list[0][2] + my_list[1][2] and check if this value is greater 0.9 .

If yes I want to stop the loop adding to my new_list the first 2 elements of the second inner list:

new_list = [['RN1', 200], ['RN2', 0.8]]

If not continue adding elements till the threshold of 0.9 is reached.

Of course this is just an example. My real lists can be a lot bigger and the process should be iterative.

I have tried different possibilities but all of them are not working. For example I have done:

sum_percentage = 0.0

new_list =[]

    for i in old_list:

        if sum_percentage <= 0.9:

            sum_percentage = sum_percentage + i[2]

        new_list.append([i[0], i[1]])

And other variants of this...Now I am stuck.

Any tips?

Thanks a lot

Answer 1

This'll do the job for you:

sum_percentage = 0.0
new_list = []
for i in old_list:
    new_list.append(i[:2])
    sum_percentage += i[2]
    if sum_percentage >= 0.9:
        break

I think it's self-explanatory, but if you're confused about anything, let me know and I'll expand this answer.