如何访问2d数组的每个元素，然后替换它们？

Question

arr = [['.' for i in range(4)] for j in range(4)]

for line, i in enumerate(arr):
    for column, j in enumerate(i):
        print(j, 'at column', column+1, 'line', line+1) # we can know which  
                                                        # postition takes 
                                                        # every element

How out of loop to check if coordinate is different with another coordinate.

What I want to get in final:

pseudocode:

#arr[x][y]
arr[1][0] = 'new'
if arr[1][4] - arr[1][0] == 4: # i.e. coord are different by `y` on 4 pos 
    arr[1][4] = 'new'`

               # Before || After
[[' ', 'new', ' ', ' '],||  [[' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' ']]   ||   [' ', 'new', ' ', ' ']]

OR

#arr[x][y]
arr[0][0] = 'new'
if arr[3][0] - arr[0][0] == 3: # i.e. coord are different by `x` on 3 pos 
    arr[3][0] = 'new'`

               # Before || After
[['new', ' ', ' ', ' '],||  [[' ', ' ', ' ', 'new'],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' '],   ||   [' ', ' ', ' ', ' '],
 [' ', ' ', ' ', ' ']]   ||   [' ', ' ', ' ', ' ']]

Necessarily need to know which list in main list takes position, but how it does outside of loop without numpy, using native python?

Answer 1

Question : How out of loop to check if coordinate is different with another coordinate.

Define the coordinate's using tuple , then compare the tuples :

RC = (1,4)
RC2 = (1,0)

if RC == RC2:
    print('Equal')
else:
    print('Different')

Type list is 0 Based You have a list of lists.

RC Coordinate System, the same as with Excel
R == index of list in list == y == Row
C == index inside a list == x == Column

        A    B    C    D
C =>     0    1    2    3
    ----------------------
R:0 | [0.0, 0.1, 0.2, 0.3]
R:1 | [1.0, 1.1, 1.2, 1.3]
R:2 | [2.0, 2.1, 2.2, 2.3]
R:3 | [3.0, 3.1, 3.2, 3.3]

---

Use the opposite

#arr[y][x]

The first index=y is the index of a list in arr , alias row .
The second index=x is the index inside the list selected with y , alias column .