英文:
Confused about creating a result matrix for NxN matrix transposition in Python
问题
NxN矩阵转置在将"result"矩阵设置为输入矩阵时会产生错误答案。
def flippingMatrix(matrix):
result = [[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in result:
print(i)
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i] = matrix[i][j]
for i in result:
print(i)
# //主程序//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
result = flippingMatrix(matrix)
现在,如果运行此程序,我们输入'N',即行和列的数量。然后在下一行输入矩阵元素。这是我提供的输入:
2
1 2
3 4
输出结果:
[0, 0] # 这是我创建的结果矩阵
[0, 0]
[1, 3] # 最终的结果矩阵
[2, 4]
问题在于:如果我将
"result=matrix"
而不是
result=[[0 for i in range(len(matrix))] for j in range(len(matrix))]
我会得到错误的答案。我假设我们只需要一个NxN矩阵的布局作为结果矩阵。那么为什么将结果设置为输入会导致错误答案呢?反正它最终都会被覆盖。
对于与之前相同的输入,我得到以下输出:
[1, 2] # 初始结果矩阵,即复制的输入矩阵
[3, 4]
[1, 2] # 最终的结果矩阵
[2, 4]
如果需要进一步解释,请留言在这个帖子上,我将尽力解释我的问题。
编辑:
我在建议进行编辑后使用的新代码如下,我仍然面临相同的问题。
def flippingMatrix(matrix):
result = matrix
for i in result:
print(i)
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i] = matrix[i][j]
return result
# //主程序//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
result = flippingMatrix(matrix)
print(result)
这里的问题可能是赋值语句 result = matrix。但我认为结果矩阵不需要为零才能被重写。
英文:
NxN Matrix transposing gives wrong answers upon making "result" matrix = input matrix
Novice programmer here. I am trying to transpose a NxN matrix. Putting the code here to make the problem clear:
def flippingMatrix(matrix):
result=[[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in result:
print(i)
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i]=matrix[i][j]
for i in result:
print(i)
# //Main Program//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
result = flippingMatrix(matrix)
Now, if we run this program, we input 'N' which is no. of rows and columns. And in the next line, elements into the matrix. This is the input that I gave:
2
1 2
3 4
The output:
[0, 0] //This is the result matrix that I made//
[0, 0]
[1, 3] //The final result matrix//
[2, 4]
Coming to the problem: If, I assign the
"result=matrix"
instead of
result=[[0 for i in range(len(matrix))] for j in range(len(matrix))]
I get the wrong answer. I am assuming that we need a result matrix as only a layout of NxN matrix. Then why does making the result same as input gives wrong answer? It is anyways going to be overwritten.
With the same input as earlier, I get the following output:
[1, 2] //Initial result matrix which is the copied input matrix//
[3, 4]
[1, 2] //The final result matrix//
[2, 4]
I apologize if the problem is a bit unclear, I tried my best. If anyone needs further explanation, comment on this post and I will try to explain my problem
EDIT:
The new code that I am using after I was suggested an edit. The new code is as follows and I am facing the same problem
def flippingMatrix(matrix):
result=matrix
for i in result:
print(i)
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i]=matrix[i][j]
return result
# //Main Program//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
result = flippingMatrix(matrix)
print(result)
Now the problem here might be because of the assignment statement result = matrix. But I don't think result matrix should be zero in order to be rewritten.
答案1
得分: 0
你的函数应该有一个返回值。如果你在函数内部分配了 matrix=result
,它不会传播到函数外部,这只是一个引用/指针分配。每个矩阵的值不会被复制。
尝试:
def flippingMatrix(matrix):
result = [[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i] = matrix[i][j]
return result
# //主程序//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
print(matrix)
result = flippingMatrix(matrix)
print(result)
在这里测试 n = 3:
def flippingMatrix(matrix):
result = [[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i] = matrix[i][j]
return result
# //主程序//
n = 3
matrix = [[i + j * n for i in range(n)] for j in range(3)]
print(matrix) # 返回 [[0, 1, 2], [3, 4, 5], [6, 7, 8]]
matrix = flippingMatrix(matrix)
print(matrix) # 返回 [[0, 3, 6], [1, 4, 7], [2, 5, 8]]
英文:
Your function should have a return, if you assign matrix=result
inside its scope, this won't propagate outside of the function, it's only a reference/pointer assignment. The values of each matrix is not copied.
Try:
def flippingMatrix(matrix):
result=[[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i]=matrix[i][j]
return result
# //Main Program//
n = int(input().strip())
matrix = []
for i in range(n):
matrix.append(list(map(int, input().rstrip().split())))
print(matrix)
result = flippingMatrix(matrix)
print( result)
Tested here for n = 3:
def flippingMatrix(matrix):
result=[[0 for i in range(len(matrix))] for j in range(len(matrix))]
for i in range(len(matrix)):
for j in range(len(matrix)):
result[j][i] = matrix[i][j]
return result
# //Main Program//
n = 3
matrix = [[i+j*n for i in range(n)] for j in range(3)]
print( matrix) # returns [[0, 1, 2], [3, 4, 5], [6, 7, 8]]
matrix = flippingMatrix(matrix)
print( matrix) # returns [[0, 3, 6], [1, 4, 7], [2, 5, 8]]
答案2
得分: 0
以下是要翻译的内容:
所以我通过与 @slothrop 在评论中交流了解到,Python 不会轻易复制嵌套列表。为了创建一个独立的二维数组副本,我必须使用不同的命令,如下所示:
b = copy.deepcopy(a)
b = [item[:] for item in a]
b = [item.copy() for item in a]
b = [list(item) for item in a]
b = [copy.copy(item) for item in a]
b = []; b.extens[a]
这里是相关问题的链接:这里。
英文:
So I learned by talking in comments with @slothrop, Python doesn't take copying of lists inside of lists lightly. In order to make a copy, I have to use different commands like so that it actually makes an independent 2D array:
b = copy.deepcopy(a)
b = [item[:] for item in a]
b = [item.copy() for item in a]
b = [list(item) for item in a]
b = [copy.copy(item) for item in a]
b = []; b.extens[a]
The link to such other question is here.
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