Python：查找列表列表的最大值和索引

Question

I have a list of list of list in python, which looks like this :

my_list = [ [[1,2,3],[4,3,2]] , [[2,1,9],[8,1,2]] , [[5,4,3],[1,6,7]] , ...]

would like to retrieve the max value of the list and its three indices.

I have seen how to do it for a list of list :

max_value, max_index = max((x, (i, j))
                           for i, row in enumerate(my_list)
                           for j, x in enumerate(row))

but I don't understand how to adapt it for a 3rd list.

---

Another question : Is there an easy way to apply the following operation on all the elements of my list ?

my_list = my_list - my_list[0] * 2

Answer 1

Just extend the concept?

max_value, max_index = max((x, (i, j, k))
                       for i, row in enumerate(my_list)
                       for j, col in enumerate(row))
                       for k, x in enumerate(col))

For your second question, look at the map function; it's designed for just this purpose.

map(lambda x: x - my_list[0] - 2, my_list)

Example:

>>> my_list = [5, 20, 22, 13, 8, 1000]
>>> map(lambda x: x - my_list[0] * 2, my_list)
[-5, 10, 12, 3, -2, 990]

Answer 2

Why not use numpy ?

import numpy as np

lst = [[[1,2,3],[4,3,2]] , [[2,1,9],[8,1,2]] , [[5,4,3],[1,6,7]]]

a = np.array(lst)                       # Create numpy array from list

>>> a
Out[]:
array([[[1, 2, 3],
        [4, 3, 2]],

       [[2, 1, 9],
        [8, 1, 2]],

       [[5, 4, 3],
        [1, 6, 7]]])

>>> a.tolist()                          # And convert back to list if needed
Out[]: [[[1, 2, 3], [4, 3, 2]], [[2, 1, 9], [8, 1, 2]], [[5, 4, 3], [1, 6, 7]]]

>>> a.tolist() == lst
Out[]: True

Get the indices of the maximum with:

>>> np.argwhere(a == a.max())           # Indices where a is maximum
Out[]: array([[1, 0, 2]], dtype=int64)

And apply your operation with:

a -= a[0] * 2                           # Apply operation inplace

>>> a
Out[]:
array([[[-1, -2, -3],
        [-4, -3, -2]],

       [[ 0, -3,  3],
        [ 0, -5, -2]],

       [[ 3,  0, -3],
        [-7,  0,  3]]])

Answer 3

So the solution I designed for the first problem first finds the max list from each row in the 3d list:

my_max_list =  map(max, my_list)

Then incorporates your original solution for find the max element in a list of lists

max_value, max_index = max((x, (i, j))
                       for i, row in enumerate(my_max_list)
                       for j, x in enumerate(row)) 

For the second problem you can just use the map function

map(lambda x: x - my_list[0] * 2, my_list)

Answer 4

You can try this:

my_list = [ [[1,2,3],[4,3,2]] , [[2,1,9],[8,1,2]] , [[5,4,3],[1,6,7]]]
maximum, the_index = [(a, i) for i, a in enumerate(my_list) if a == max(my_list)][0]
new_list = [[[c-b[0]*2 for c in b] for b in i] for i in my_list]