## Fill NaN cell with mean of eight surrounding cells in grid data in matlab

### Shakir Hussain (view profile)

on 21 Apr 2018
Latest activity Edited by Jan

on 25 Apr 2018

### Jan (view profile)

I am trying to fill the NaN values of grid data with 8 surrounding values but could not understand, what is going wrong here in my matlab code. The data is 752*891*11 %%% (11 years precipitation of 752*891 cells).
for i = 2 : 752
for j = 2 : 891
for k = 1 : 11
if isnan(data(i,j,k)) == 1
data(i,j,k) = nanmean(nanmean(data(i-2:i+2,j-2:j+2,k-2:k+2)));
end
end
end
end

on 21 Apr 2018
Edited by Jan

### Jan (view profile)

on 25 Apr 2018

If you want to replace a scalar based on a 3D array, you either need 3 nanmean calls:

```nanmean(nanmean(nanmean(data(i-1:i+1, j-1:j+1, k-1:k+1))))
```

with i-1:i+1, instead of i-2:i+2. This would be easier:

```if isnan(data(i,j,k))   % "== 1" is not needed
tmp         = data(i-1:i+1, j-1:j+1, k-1:k+1);  % 3D block
data(i,j,k) = nanmean(tmp(:));                  % Make it a vector
end
```

But this is a 3x3x3 neighborhood with 27 elements, not 8. I assume you mean:

```if isnan(data(i,j,k))   % "== 1" is not needed
tmp1        = data(i-1:i+1, j, k);
tmp2        = data(i:i, j-1:j+1, k);
tmp3        = data(i, j, k-1:k+1);
tmp         = [tmp1(:); tmp2(:); tmp3(:)];  % Create a vector
data(i,j,k) = nanmean(tmp);
end
```

Because the center point data(i,j,k) is included 3 times, but ignored by nanmean, you have 6 neighbors now, not 8.

So please explain again, what you exactly want.

Shakir Hussain

### Shakir Hussain (view profile)

on 24 Apr 2018
The above four preference is for single year and wants to repeat the same way for 11 years. We have both positive and negative values of temperature and your above given code is pop up with (Subscript indices must either be real positive integers or logicals.) error.
Jan

### Jan (view profile)

on 24 Apr 2018

When you access the index i-2:i+2, the loop for i must start at 3, not at 2, because 0 is not a valid index. And the loop must stop at size(data, 1) - 2. Equivalently for j.

Please post a copy of the complete message, if you mention an error in the forum.

Shakir Hussain

### Shakir Hussain (view profile)

on 25 Apr 2018
Thank you jan The problem has solved ### Walter Roberson (view profile)

on 22 Apr 2018

```means = conv2(YourMatrix, [1 1 1;1 0 1;1 1 1]/8,'same') ;
```

No loops needed.

Note: you would need a little adjustment to handle a nan on the edge of the matrix, to calculate the means properly.

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Walter Roberson

### Walter Roberson (view profile)

on 22 Apr 2018
Ah, good point, the 0 * nan at the point itself makes the conv2() result into nan.
Jan

### Jan (view profile)

on 22 Apr 2018

A solution to use conv2 with NaNs:

```nanX    = isnan(X);
X(nanX) = 0;
mask    = [1 1 1; 1 0 1; 1 1 1];
means   = conv2(X,     mask, 'same') ./ ...