如何在 Python 中输入矩阵(二维列表)? [英] How to input matrix (2D list) in Python?

问题描述

我尝试创建此代码以输入 m × n 矩阵.我打算输入 [[1,2,3],[4,5,6]] 但代码产生 [[[4,5,6],[4,5,6]].当我输入其他 m × n 矩阵时，会发生同样的事情，代码生成一个 m × n 矩阵，其行相同.

也许你可以帮我找出我的代码有什么问题.

m = int(input('行数，m = '))n = int(input('列数，n = '))矩阵 = [];列 = []# 初始化行数对于范围内的 i (0,m):矩阵 += [0]# 初始化列数对于范围 (0,n) 中的 j:列 += [0]# 初始化矩阵对于 i 在范围 (0,m) 中:矩阵[i] = 列对于 i 在范围 (0,m) 中:对于范围 (0,n) 中的 j:打印('行中的条目:'，i+1，'列:'，j+1)矩阵[i][j] = int(input())打印(矩阵)

解决方案

问题出在初始化步骤.

 for i in range (0,m):矩阵[i] = 列

这段代码实际上使 matrix 的每一行都指向同一个 columns 对象.如果任何列中的任何项目发生更改 - 每隔一列都会更改:

<预><代码>>>>对于 i 在范围 (0,m) 中:...矩阵[i] = 列...>>>矩阵[[0, 0, 0], [0, 0, 0]]>>>矩阵[1][1] = 2>>>矩阵[[0, 2, 0], [0, 2, 0]]

您可以在嵌套循环中初始化矩阵，如下所示:

矩阵 = []对于范围内的 i (0,m):矩阵.附加([])对于范围内的 j (0,n):矩阵[i].append(0)

或者，在单行中使用列表理解:

matrix = [[0 for j in range(n)] for i in range(m)]

或:

matrix = [x[:] for x in [[0]*n]*m]

另见:

• 如何在 Python 中初始化二维数组?

希望有所帮助.

I tried to create this code to input an m by n matrix. I intended to input [[1,2,3],[4,5,6]] but the code yields [[4,5,6],[4,5,6]. Same things happen when I input other m by n matrix, the code yields an m by n matrix whose rows are identical.

Perhaps you can help me to find what is wrong with my code.

m = int(input('number of rows, m = '))
n = int(input('number of columns, n = '))
matrix = []; columns = []
# initialize the number of rows
for i in range(0,m):
  matrix += [0]
# initialize the number of columns
for j in range (0,n):
  columns += [0]
# initialize the matrix
for i in range (0,m):
  matrix[i] = columns
for i in range (0,m):
  for j in range (0,n):
    print ('entry in row: ',i+1,' column: ',j+1)
    matrix[i][j] = int(input())
print (matrix)

解决方案

The problem is on the initialization step.

for i in range (0,m):
  matrix[i] = columns

This code actually makes every row of your matrix refer to the same columns object. If any item in any column changes - every other column will change:

>>> for i in range (0,m):
...     matrix[i] = columns
... 
>>> matrix
[[0, 0, 0], [0, 0, 0]]
>>> matrix[1][1] = 2
>>> matrix
[[0, 2, 0], [0, 2, 0]]

You can initialize your matrix in a nested loop, like this:

matrix = []
for i in range(0,m):
    matrix.append([])
    for j in range(0,n):
        matrix[i].append(0)

or, in a one-liner by using list comprehension:

matrix = [[0 for j in range(n)] for i in range(m)]

or:

matrix = [x[:] for x in [[0]*n]*m]

See also:

• How to initialize a two-dimensional array in Python?

Hope that helps.

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