How to access the length of an inner element in a 2D/3D list?-CodePudding

This function returns the maximum number of elements of a list, of a list, in a list. I think this is a correct approach but I keep getting the error:

'TypeError: list indices must be integers or slices, not lists'

Here's the list:

list = [[0, [1, 2, 3]], [1, [0, 1, -3, 8, 5]], [2, [0, 7, 2, 1, -5]], [3, [0, 4, 1, -9]], [4, [0, 6, -2, 3]],
[5, [0]], [6, [0, 2, -1, 8]], [7, [0, -7, 3]], [8, [0, 8, 5, 6, 3]], [9, [0, -4, 1, 9]]]

Here's the function:

def max_inner_list_length(list):

    maximum = 0

    for i in list:
        if len(list[i][1]) > maximum:
            maximum = len(list[i][1])

    return maximum

Example:

max_inner_list_length(list)

Expected output: 5

Actual output: TypeError: list indices must be integers or slices, not lists

CodePudding user response：

If you need to find the maximum length of the list then you can use this below snippet it returns the maximum length i.e., 5 in the given case. I failed to understand len(network[i][1]) part you can edit the remaining part by yourself. If you need further help feel free to comment.

def max_inner_list_length(list):
   maximum = 0
   for i in range(len(list)):
      if len(list[i][1]) > maximum:
         maximum = len(list[i][1])       
return maximum
print(max_inner_list_length(list))

I think you are assigning that len(network[i][1]) to the maximum that is why you are not getting the desired result. Also, one suggestion is never to use the inbuilt function name as variables.

CodePudding user response：

There are two issues in your code.
The first one inducing the error is that for i in List will iterate through the values of list which aren't integers. However you put L[i] right below in which i has to be an integer.
The second one is the fact that list is a reserved name in python refering to the type list. Thus, you should not name your list list (or a string str) but rather L.

You should replace your code by :

def max_inner_list_length(L):
    
    maximum = 0
    for i in range(len(L)):
        if len(L[i][1]) > maximum:
            maximum = len(L[i][1]) #I suppose network is a variable
                                   #outside the function context,
    return maximum                 #which should be replace by L

Or you can keep your line in the for loop by changing the following line, like so:

def max_inner_list_length(L):
    
    maximum = 0
    for i in L:
        if len(i[1]) > maximum:
            maximum = len(i[1])
    return maximum

CodePudding user response：

It is bad practice to name variables after inbuilt python functions, as it overwrites them. I have renamed list to lst for this answer.

Currently, you are iterating through every element in the list as i, so when calling lst[i][1], the first i will be (0, [1, 2, 3]) which isn't a valid index. You can check this by running:

for i in lst:
    print(i)

You will need to change your for loop to be for i in range(len(lst)), then you will be looping through the indexes instead of the elements, as below:

def max_inner_list_length(lst):

    maximum = 0

    for i in range(len(lst)):
        if len(lst[i][1]) > maximum:
            maximum = len(network[i][1])

    return maximum

Alternatively, you can use i as is, and use that instead of lst[i], as below:

for i in range(len(lst)):
    if len(i[1]) > maximum:

However this probably won't work as required for your network[i][1] line, so the first approach is best for your problem.