TypeError：'float' object 在尝试对列表列表中的索引进行排序时不可下标

Question

In python 3.0 I am currently trying to use my insertion sort algorithm to sort a list of lists I have by their 2nd element (1st index). For example, I would like to sort a list like this according to the value of the 2nd element in descending order.

pre-sort:

list = [ ["Name1", 10.0, 9.5, 8.6, 4.0],
         ["Name2", 14.5, 9.1, 4.2, 0.6],
         ["Name3", 9.9, 42.0, 9.1, 4.1],
        .....]

post-sort:

list = [ ["Name2", 14.5, 9.1, 4.2, 0.6],
         ["Name1", 10.0, 9.5, 8.6, 4.0],
         ["Name3", 9.9, 42.0, 9.1, 4.1],
        .....]

My current insertion sort method looks like this:

def sort_points(a_list):
      """Sorts in descending order."""
      for index in range(1, len(a_list)):
            value = a_list[index][1]
            pos = index - 1
            while pos >= 0 and a_list[pos][1] < value:
                  a_list[pos + 1] = a_list[pos]
                  pos -= 1
            a_list[pos + 1] = value

And when I try to run the code I am given the following error:

Traceback (most recent call last):

  sort_points(allstars_2021)
File "C:/Users/Michael/PycharmProjects/NBAstats/CompareStats.py", line 16, in sort_points
  while pos >= 0 and a_list[pos][1] < value:
TypeError: 'float' object is not subscriptable

Not sure what I am doing wrong here because I adjusted my insertion_sort algorithm I have used previously with float values but never in the scenario of sorting in element within a list of a list. Any help would be greatly appreciated, Thank you!

Answer 1

This is not a answer, just want to show you how I reproduce this.

In [4]: list = [ ["Name1", 10.0, 9.5, 8.6, 4.0],
   ...:          ["Name2", 14.5, 9.1, 4.2, 0.6],
   ...:          ["Name3", 9.9, 42.0, 9.1, 4.1],]

In [5]: def sort_points(a_list):
   ...:       """Sorts in descending order."""
   ...:       for index in range(1, len(a_list)):
   ...:             value = a_list[index][1]
   ...:             pos = index - 1
   ...:             while pos >= 0 and a_list[pos][1] < value:
   ...:                   a_list[pos + 1] = a_list[pos]
   ...:                   pos -= 1
   ...:             a_list[pos + 1] = value
   ...:

In [6]: sort_points(list)

In [7]: list
Out[7]: [14.5, ['Name1', 10.0, 9.5, 8.6, 4.0], 9.9]

In [8]: sort_points(list)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-8-5a1fa048546f> in <module>
----> 1 sort_points(list)

<ipython-input-5-fc8e50df198d> in sort_points(a_list)
      4             value = a_list[index][1]
      5             pos = index - 1
----> 6             while pos >= 0 and a_list[pos][1] < value:
      7                   a_list[pos + 1] = a_list[pos]
      8                   pos -= 1

TypeError: 'float' object is not subscriptable

if you can give exact input for your function, I can try to fix that.

Answer 2

In the first iteration, your pos == 0, and your a_list[pos][1] == value so it never enters the loop.

and at the end of the loop, you replace the 2nd index a_list[pos+1] that is a_list[2] with a float value. a_list[pos+1] = value

now in the 2nd iteration, when your code reaches your while loop, it tries to access a_list[2][1] , but you already replace a_list[2] with a float value 14.0, and therefore it throws the error that you are trying to subscript a float value.