how do you replace only a certain number of items in a list randomly? - python-3.x

Question

board = []
for x in range(0,8):
board.append(["0"] * 8)
def print_board(board):
for row in board:
print(" ".join(row))
this code creates a grid of zeros but I wish to replace 5 of them with ones and another five with twos
does anyone know a way to do this?

Answer 1

If you want to randomly set some coordinates with "1" and "2", you can do it like this:
import random
board = []
for x in range(0, 8):
board.append(["0"] * 8)
def print_board(board):
for row in board:
print(" ".join(row))
def generate_coordinates(x, y, k):
coordinates = [(i, j) for i in range(x) for j in range(y)]
random.shuffle(coordinates)
return coordinates[:k]
coo = generate_coordinates(8, 8, 10)
ones = coo[:5]
twos = coo[5:]
for i, j in ones:
board[i][j] = "1"
for i, j in twos:
board[i][j] = "2"
print_board(board)
Output
0 1 0 0 0 0 0 0
0 1 0 0 0 0 0 0
0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 0
0 0 2 0 0 0 0 0
1 0 0 0 2 0 0 0
0 0 0 0 2 0 0 2
2 0 0 0 0 0 0 1
Notes:
The code above generates a random sample each time so the output will be different each time (to generate the same use random.seed(42), you can change 42 for any number you want.
The function generate_coordinates receives x (number of rows), y (number of columns) and k (the number of coordinates to pick). It generates a sequence of coordinates of x*y, shuffles it and picks the k first.
In your specific case x = 8, y = 8 and k = 10 (5 for the ones and 5 for the twos)
Finally, this picks the positions for the ones and twos and changes the values:
ones = coo[:5]
twos = coo[5:]
for i, j in ones:
board[i][j] = "1"
for i, j in twos:
board[i][j] = "2"