更改列表的元素以匹配另一个列表

Question

I am trying to iterate through a list of list and increase the first element in each sublist until it matches an integer on another list...

list1=[[2, 13, 22, 40], [8, 13, 22, 40], [24, 13, 22, 40]]
reference_list = [5, 10, 30]
for i in list1: 
    while (i[0] != i) in reference_list:    
        i[0] = i[0] + 1
print(list1)

Right now my output is:

[[2, 13, 22, 40], [8, 13, 22, 40], [24, 13, 22, 40]]

(Nothing is getting modified) My desired output is:

[[5, 13, 22, 40], [10, 13, 22, 40], [30, 13, 22, 40]]

(so that the first integer is increased until it matches an integer on the reference_list)

I have dabbled using the set function but I can't seem to get that to work.

Any ideas are appreciated!

Answer 1

This should work, you "while" condition was using the same iterator for two different lists

list1=[[2,13,22,40],[8,13,22,40],[24,13,22,40]]
reference_list=[5, 10, 30]
for i in list1:
    while i[0] not in reference_list:
        i[0]=i[0]+1
print(list1)

But as @GrzegorzBokota said, if the first element of list1 is bigger than all of the elements in the reference list, you will have an infinite loop, be careful.

Answer 2

if you replace the reference list by a numpy.array , you can directly index the element which is the next bigger one:

import numpy as np

list1 = [[2,13,22,40],[8,13,22,40],[24,13,22,40]]
reference_list = np.array([5, 10, 30])
for i in list1:
    i[0] = reference_list[reference_list>=i[0]][0]
print(list1)

# [[5, 13, 22, 40], [10, 13, 22, 40], [30, 13, 22, 40]]

Note that this also does not address the problem which occurs if your reference does not provide the biggest value.
But this can be solved by checking if the list of all bigger values is empty:

list1 = [[200,13,22,40],[8,13,22,40],[24,13,22,40]]
reference_list = np.array([5, 10, 30])
for i in list1:
    next_bigger = list(reference_list[reference_list>=i[0]])
    if next_bigger:
        i[0] = next_bigger[0]
print(list1)
# [[200, 13, 22, 40], [10, 13, 22, 40], [30, 13, 22, 40]]

Answer 3

If you want to quantize the first element of each sublist to one of the entries in the reference_list, you could do it with a list comprehension:

list1=[[2,13,22,40],[8,13,22,40],[24,13,22,40]]
reference_list=[5, 10, 30]
list1 = [ [next((r for r in reference_list if r>=v[0]),v[0])]+v[1:] for v in list1 ]
print(list1)

Your question and example could also be interpreted to mean that each entry in the reference list corresponds to a list at the same position in the list of lists. If that is the case, you can use zip to traverse both lists in parallel:

list1 = [ [max(r,v[0])]+v[1:] for r,v in zip(reference_list,list1) ]