ภาพรวม
จาก square matrix (list of lists ขนาด n x n) ให้ลบ element บน main diagonal (index i,i) ออกจากแต่ละแถว
ตัวอย่างโค้ด
my_list = [
[45, 67, 85, 42, 11],
[78, 99, 10, 13, 0],
[91, 23, 23, 64, 23],
[91, 11, 22, 14, 35]
]
print("The list is:", my_list)
my_result = []
for i, row in enumerate(my_list):
# เก็บ element ที่ column index != row index
new_row = [val for j, val in enumerate(row) if j != i]
my_result.append(new_row)
print("The resultant matrix is:", my_result)
ผลลัพธ์
The list is: [[45, 67, 85, 42, 11], [78, 99, 10, 13, 0], [91, 23, 23, 64, 23], [91, 11, 22, 14, 35]]
The resultant matrix is: [[67, 85, 42, 11], [78, 10, 13, 0], [91, 23, 64, 23], [91, 11, 22, 35]]
คำอธิบาย
| Row i | Original | Remove index i | Result |
|---|---|---|---|
| 0 | [45, 67, 85, 42, 11] | index 0 (45) | [67, 85, 42, 11] |
| 1 | [78, 99, 10, 13, 0] | index 1 (99) | [78, 10, 13, 0] |
| 2 | [91, 23, 23, 64, 23] | index 2 (23) | [91, 23, 64, 23] |
| 3 | [91, 11, 22, 14, 35] | index 3 (14) | [91, 11, 22, 35] |
NumPy Version (เร็วกว่าสำหรับ Matrix ใหญ่)
import numpy as np
arr = np.array(my_list)
# Boolean mask ไม่ใช่ diagonal
mask = ~np.eye(arr.shape[0], dtype=bool)
result = arr[mask].reshape(arr.shape[0], -1)
print(result)
ประยุกต์: Secondary Diagonal
# ลบ secondary diagonal (i, n-1-i)
new_row = [val for j, val in enumerate(row) if j != len(row) - 1 - i]
