将矩阵的元素与整数相乘以创建新矩阵

Question

I have a matrix M, for which I need to return a tuple (i,j) which gives me the index (row,column) of the first maximum value in the matrix.

Tried this, but gives me a type error that int is not iterable.

Would be very grateful for your help / advice on this.

def matrix_max_index(M):
  m=len(M)
  n=len(M[0])
  for i in range(0,m):
    for j in range (0,n):    
        if M[i][j] ==  max(M[i][j]):
          return (i,j)

for example: if input is M = [[0, 3, 2, 4], [2, 3, 5, 5], [5, 1, 2, 3]] returns (1,2)

Answer 1

Use max to find the overall maximum and then next to find the first coordinate matching it:

def matrix_max_index(M):
    # find the overall maximum 
    ma = max(e for row in M for e in row)

    # find the first matching value
    res = next((i, j) for i, row in enumerate(M) for j, e in enumerate(row) if e == ma)
    return res


M = [[0, 3, 2, 4], [2, 3, 5, 5], [5, 1, 2, 3]]

print(matrix_max_index(M))

Output

(1, 2)

As an alternative use the key parameter of max to map the indices to their corresponding value and pick the one with the maximum:

def matrix_max_index(M):
    rows = len(M)
    cols = len(M[0])
    res = max(((i, j) for i in range(rows) for j in range(cols)), key=lambda x: M[x[0]][x[1]])
    return res

Answer 2

The following will work:

def matrix_max_index(M):
    m_val = coords = None
    for r, row in enumerate(M):
        for c, val in enumerate(row):
            if m_val is None or val > m_val:
                m_val = val
                coords = r, c
    return coords

You have to keep track of the current maximum and update maximum value and coordinates as necessary. You can only return at the end once you have visited all cells.

Some docs:

• enumerate