Finding neighbours in a two-dimensional array

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Is there an easy way of finding the neighbours (that is, the eight elements around an element) of an element in a two-dimensional array? Short of just subtracting and adding to the index in different combinations, like this:

array[i-1][i]
array[i-1][i-1]
array[i][i-1]
array[i+1][i]

... And so on.

(pseudo-code)

row_limit = count(array);
if(row_limit > 0){
  column_limit = count(array[0]);
  for(x = max(0, i-1); x <= min(i+1, row_limit); x++){
    for(y = max(0, j-1); y <= min(j+1, column_limit); y++){
      if(x != i || y != j){
        print array[x][y];
      }
    }
  }
}

Of course, that takes almost as many lines as the original hard-coded solution, but with this one you can extend the "neighborhood" as much as you can (2-3 or more cells away)

Problem of 8 Neighbours of an element in a 2-D Matrix , Problem of 8 Neighbours of an element in a 2-D Matrix For second iteration, cell (0, 0) was 0 but this time it is surrounded by two cells Dimension of Array. I've a 2D grid of 75rows by 75 cols, I draw symbols of 2 colors (red and blue) on users clicks, it works fine but I'm stuck on a major problem I want to find the neighbor of those symbols: Example when the user click on a cell, it prints a symbol (oval) now I want that click also checks in its neighbors if the cell are occupied or empty, if

I think Ben is correct in his approach, though I might reorder it, to possibly improve locality.

array[i-1][j-1]
array[i-1][j]
array[i-1][j+1]

array[i][j-1]
array[i][j+1]

array[i+1][j-1]
array[i+1][j]
array[i+1][j+1]

One trick to avoid bounds checking issues, is to make the array dimensions 2 larger than needed. So, a little matrix like this

3 1 4
1 5 9
2 6 5

is actually implemented as

0 0 0 0 0
0 3 1 4 0
0 1 5 9 0
0 2 6 5 0
0 0 0 0 0 

then while summing, I can subscript from 1 to 3 in both dimensions, and the array references above are guaranteed to be valid, and have no effect on the final sum. I am assuming c, and zero based subscripts for the example

How to find neighbours (including boundary conditions) in 2D array , set up a grid, then use a recursive function that increases the x vaue, then the y value, both times checking if the element at x2, y2 is a boundary whereas x2 and � Is there an easy way of finding the neighbours (that is, the eight elements around an element) of an element in a two-dimensional array? Short of just subtracting and adding to the index in different combinations, like this: array [i-1] [i] array [i-1] [i-1] array [i] [i-1] array [i+1] [i]

an alternative to @SebaGR, if your language supports this:

var deltas = { {x=-1, y=-1}, {x=0, y=-1}, {x=1, y=-1},
               {x=-1, y=0},               {x=1, y=0},
               {x=-1, y=1},  {x=0, y=1},  {x=1, y=1} };
foreach (var delta in deltas)
{
    if (x+delta.x < 0 || x + delta.x >= array.GetLength(0) ||
        y+delta.y < 0 || y + delta.y >= array.GetLength(1))
        continue;

    Console.WriteLine("{0}", array[x + delta.x, y + delta.y]);
}

Slight advantage in readability, possible performance if you can statically allocate the deltas.

How to get the valid neighbors of a 2D array? : javahelp, I am trying to count the # neighbors of the current index (cells[i][j]) that have a value of 'true'. int [][] array = new int [maxRows][maxCols]; int count = 0; for (int i = 0 ; i < maxRows ; i++) Having trouble finding an eloquent solution, any ideas ? So, I have a 4x4 2D array (it will always be these dimensions). Starting with a location on the array, some row and column, I want to find all of its valid neighbors. So far, I have a really clunky implementation.

Here is a working Javascript example from @seb original pseudo code:

function findingNeighbors(myArray, i, j) {
  var rowLimit = myArray.length-1;
  var columnLimit = myArray[0].length-1;

  for(var x = Math.max(0, i-1); x <= Math.min(i+1, rowLimit); x++) {
    for(var y = Math.max(0, j-1); y <= Math.min(j+1, columnLimit); y++) {
      if(x !== i || y !== j) {
        console.log(myArray[x][y]);
      }
    }
  }
}

Checking the neighbour values of arrays, 2d array check neighbors python find neighbors in 2d array python find the alphabet with highest neighbors python finding neighbours in a two-dimensional � Let's say I have an array list of four java 2d arrays with the same dimensions. I will join the 2d arrays at index 0 and 1 of the array list and then join the arrays at indexes 2 and 3 of the array list. Then I will add these two joined arrays to the variable that is also another list of 2d arrays called "currentMatrices".

array[i][j] has neighbors

array[i-1][j]
array[i][j-1]
array[i-1][j-1]
array[i+1][j]
array[i][j+1]
array[i+1][j+1]
array[i+1][j-1]
array[i-1][j+1]

That's probably the fastest/easiest way is to just list all possible neighbors. Make sure to do index out of bound checking though.

Some languages might offer a shortcut way of doing this, but I don't know of any.

Getting the neighbors of a Point in a 2D grid, For example, take Minesweeper Flags (where the objective is to find the List< Point> neighbors = new ArrayList<Point>(); for (Point neighbor� Each array element has eight neighbours, if it is not on the "edge of the grid", as in, if it does not have a row or column value of 0 or a row or column value of array.length-1 Now, if a element has the same value as 3 of its neighbours a counter variable needs to be incremented.

Find sum of neighbors in a 2D array, Don't return if there is an error, throw the error. if(i<0 || j< 0) { throw new Error(" Invalid Index"); } if(i>rowLimit || j> columnLimit){ throw new� c2 (1:N)= {2}; offsets=sub2ind (s,c1 {:}) - sub2ind (s,c2 {:}) Now, for any linear index in your matrix L, you can get all its neighbors by doing. neighbors = yourmatrix (L+offsets) It won't work at the edges of the matrix, but you can take care of that by padding the edges first.

How to find all neighbours of an element in N-dimensional matrix , How to find all neighbours of an element in N-dimensional matrix. Follow Does this happen even when you pad the array, as described above? So 2D gives 3 *3-1 = 8 neighbors, 3D gives 26 neighbors, 4D gives 80 neighbors, etc. neighborSum = sumOfNeighbors (r, c) image [r] [c] = neighborSum / neighborCount. "sumOfNeighbors" has to access the 2D image array. If you then compute the average and put it back into the same image array you have a situation where the average you created is now used in a subsequent call to sumOfNeighbors ().

Finding neighbours in a matrix - MATLAB Answers, Learn more about matrix, neighbours. I'm guessing you're not trying to find the neighbors simply to have a list of Let a - your double array. You can improve iterating over the array by using np.ndenumerate to get the current coordinates and current item. From the coordinates you can derive the neighbouring elements. You can also use inverse checking to only set the respective field to False if a neighbor does not match:

Comments
  • Add code to the if statement to check upper and lower bounds and it's perfect.
  • Not sure he'd want to do that; he's searching for all 8 neighbors, not just vertical || horizontal. Or did I miss something?
  • Joel is saying that if you do this at the edges, without some boundry checking, you'll get an index out of bounds exception as you look for something like array[-1][4].
  • Good idea for the bounds checking, came here to see if I could avoid it in any way and this solution will do nicely!
  • Good proposal but bad style, so no upvote. Better avoid continue and use the positive condition.
  • I guess we should exclude i=j=0, and add bounds checking if needed.