定义作用于python中矩阵的函数

Question

I want to define a reasonably simple function to swap two entries in a matrix, currently I have the following code:

def swap (n[a][b] ,direction):

    if direction==1:             #to the left
        entry=n[a][b]
        n[a][b]=n[a-1][b]
        n[a-1][b]=entry

I'm struggling to find a way to make it so that when I enter a variable eg current (where current =matrix[3][2] ) the contents of the if clause act with a=3 ,b=2 on the target matrix.

Answer 1

I'm not quite sure if this is what you want, but at least it is working python code:

import numpy as np

def swap(M, a, b, direction):
     if direction == 1:
         entry = M[a,b]
         M[a,b] = M[a-1,b]
         M[a-1,b] = entry

#create a test matrix
np.random.seed(10)
n = np.random.rand(10, 100, size=(3,2))

print n
n = swap(n,2,1,1)
print n

This outputs:

[[19 25]
 [74 38]
 [99 39]]

[[19 25]
 [74 39]
 [99 38]]

So the 38 and 39 were swapped.

Answer 2

Expanding on @interjay comment, here is a working function (assuming that matrix is list of lists):

def swap(m, r, c, direction):
    if direction == 1:
        m[r][c], m[r-1][c] = m[r-1][c], m[r][c]

parameters:

• m is matrix you want to act on,
• r is a row of the element you want to swap,
• c is a column of the element you want to swap,
• direction is direction of swap.

Usage example:

A = [[1, 2], [3, 4]]
print A
swap(A, 1, 1, 1)
print A

output:

[[1, 2], [3, 4]]
[[1, 4], [3, 2]]

Also note, that usually, but not necessary, first index corresponds to row or line and second corresponds to column. In this case so swapping n[a][b] with n[a-1][b] in your code is equivalent to moving element n[a][b] upwards one row, not to the left.