How do I decrease my range in every loop when loop was executing in python

Question

I have to decrease my range in every loop end. here is an example code:

for i in range(len(array)):
    if (array[0][5] == array[i][5]):
       array2.append(array[0])
       array3.append(array[i])
       
       array.remove(array[i])
       array.remove(array[0])

this throws an error that list index out of range so I tried to add i-=1 in every remove functions end but it doesn't fix it.

I couldnt fixed it so I tried to fix this problem in another way.

n = len(array) # maybe it could be len(array) -1 for the index problem but I also tried that it didnt work.
k = len(array)-1
for n in range(n, 0, -2):
    if (array[0][5] == array[n][5]):
       array2.append(array[0])
       array3.append(array[n])
       
       array[k] = array[n]
       array[k-1] = array[0]
       k -= 2

I thought that if I do that, I shouldn't compare the last 2 values after the loop but the error is the same error : list index out of range

Solving this problem with NOT starting loop from the end is my first priority.

I want to match 2 values from 2 different arrays when arrays 2's elements equals to each other and then I have to out them off from the list because when I match 2 values I don't need them anymore. But there is a problem right there which is when I remove the element from the list, I can not reach all the values in the list because of the iteration still during.

array1 = [0,1],[0,2],[0,2],[0,2],[0,1],[0,3]
array2 = [0,1],[0,1],[0,1],[0,2],[0,2],[0,3]
for i in range(len(array1)):
   for j in range(len(array2)):
      if(array1[i][1] == array2[j][1]):
         temp_arr2.append(array1[i])
         temp_arr1.append(array2[j])
         array1.remove(array1[i])
         array2.remove(array2[j])

Answer 1

The issue is that you may not be able to control the iteration of the variable i when using it in a for loop. Your instincts are good in attempting to modify i by 1 for each remove() call, and the missing piece of the puzzle is to use a while loop instead of a for loop.

Here is code that does what your question asks using sample data for array:

        array = [
            [0,0,0,0,0,99],
            [1,0,0,0,0,33],
            [2,0,0,0,0,66],
            [3,0,0,0,0,99],
            [4,0,0,0,0,33],
            [5,0,0,0,0,66],
            [6,0,0,0,0,99],
            [7,0,0,0,0,33],
            [8,0,0,0,0,66],
            [9,0,0,0,0,99],
            [10,0,0,0,0,33]
        ]
        array2 = []
        array3 = []
        i = 0
        while i < len(array):
            if (array[0][5] == array[i][5]):
                array2.append(array[0])
                array3.append(array[i])

                array.remove(array[i])
                array.remove(array[0])
                i += 2
            i += 1
        print(f"array {array}")
        print(f"array2 {array2}")
        print(f"array3 {array3}")

Here is sample output:

array [[3, 0, 0, 0, 0, 99], [4, 0, 0, 0, 0, 33], [6, 0, 0, 0, 0, 99], [7, 0, 0, 0, 0, 33], [8, 0, 0, 0, 0, 66], [9, 0, 0, 0, 0, 99], [10, 0, 0, 0, 0, 33]]
array2 [[0, 0, 0, 0, 0, 99], [2, 0, 0, 0, 0, 66]]
array3 [[0, 0, 0, 0, 0, 99], [5, 0, 0, 0, 0, 66]]

UPDATE: Here is an updated answer based on the updated question.

It seems as though the main concern is identifying and collecting lists contained in array1 and array2 that have matching values in a particular index. The end state of array1 and array2 does not matter.

With this in mind, I suggest the following approach which uses a Python dict to identifying matches more efficiently than nested for loops, and which will create the required lists of matches. Note that it will not modify the original lists (array1 and array2).

        array1 = [[100,1],[100,2],[100,2],[100,2],[100,1],[100,3]]
        array2 = [[200,1],[200,1],[200,1],[200,2],[200,2],[200,3]]
        dict1 = {}
        for i in range(len(array1)):
            key = array1[i][1]
            if key not in dict1:
                dict1[key] = []
            dict1[key].append(i)
        temp_arr1 = []
        temp_arr2 = []
        for j in range(len(array2)):
            key = array2[j][1]
            if key in dict1:
                i = dict1[key][0]
                temp_arr2.append(array1[i])
                temp_arr1.append(array2[j])
                dict1.pop(key)
        print(temp_arr1)
        print(temp_arr2)

Here are the outputs:

[[200, 1], [200, 2], [200, 3]]
[[100, 1], [100, 2], [100, 3]]

As you can see, the first output row (temp_arr1) contains lists that were originally in array2 and the second output row (temp_arr2) contains lists that were originally in array1. This matches the updated sample code in the question.