How to expand a grid around a specific point in an matrix?

Question

I have the following array and I would like to expand an area around X and turn array elements around X from 0 to 1. Any suggestions on how to do it?

From this array

[[0,0,0,0,0,0,0],
 [0,0,0,x,0,0,0],
 [0,0,0,0,0,0,0]]

To this array

[[0,0,1,1,1,0,0],
 [0,0,1,x,1,0,0],
 [0,0,1,1,1,0,0]]

Is this a numpy array, or a plain python list? I’ll second what @azro said. — AMC, Nov 11 '19 at 21:58
Oh and how much information about `x` do you have? Is the array guaranteed to contain only zeroes and `x`? — AMC, Nov 12 '19 at 15:53

score 0 · Answer 1 · answered Dec 09 '19 at 12:49

Not the optimal solution, but works for me. I use ROS and nav_msgs/OccupancyGrid message:

    def draw_thickened_grid_point(self, index):
        indexes_arround = []
        indexes_arround.append(index + 1)
        indexes_arround.append(index - 1)
        indexes_arround.append(index + self._map_width)
        indexes_arround.append(index - self._map_width)
        indexes_arround.append(index + self._map_width+1)
        indexes_arround.append(index + self._map_width-1)
        indexes_arround.append(index - self._map_width+1)
        indexes_arround.append(index - self._map_width-1)
        self._grid.data[int(index)] = 100
        for ind in indexes_arround:
            if(self._grid.data[int(ind)] == 0):
                self._grid.data[int(ind)] = 30

score -1 · Answer 2 · answered Nov 11 '19 at 20:54

-1

Here a possible solution, it could be improved. I am really interested to see a better implemenentation.

for i in range(len(a)):
    for j in range(len(a[i])):
            if (a[i][j] =="x"):

                if(len(a)>i+1):
                    a[i+1][j] =1
                    if(len(a[i])>j+1):
                        a[i+1][j+1] =1
                    if(len(a[i])>j-1):
                        a[i+1][j-1] =1

                if(len(a)>i-1):
                    a[i-1][j] =1
                    if(len(a[i])>j+1):
                        a[i-1][j+1] =1  
                    if(len(a[i])>j-1):
                        a[i-1][j-1] =1
                if(len(a[i])>j+1):
                        a[i][j+1] =1
                if(len(a[i])>j-1):
                        a[i][j-1] =1

print(a)

answered Nov 11 '19 at 20:54

ragnar

150
1
6

This is almost certainly not the best solution. – AMC Nov 11 '19 at 21:57
As I said, it could be improved. Still better than yours ;) – ragnar Nov 12 '19 at 15:52
I haven’t written a solution because OP’s post is woefully lacking in detail and I do not wish to encourage extremely low quality questions. Also, is the array element actually the string `’x’`, or is `x` just a variable? – AMC Nov 12 '19 at 15:54

How to expand a grid around a specific point in an matrix?

2 Answers2