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Index exceeds matrix dimensions.

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Shakir Hussain
Shakir Hussain el 1 de Mayo de 2018
Comentada: Walter Roberson el 11 de Mayo de 2020
Daily 10*10 grid precipitation data of 6 days (10*10*6) includes NaN, zeros and negative values. We are trying to replace the NaN values with surrounding cell values.The below script is giving two errors and could not fix it, ("Subscript indices must either be real positive integers or logical") ("Index exceeds matrix dimensions") And the script is as
for i = 2:10;
for j = 2:10;
for k = 2:6;
if isnan(tstsample(i,j,k))
tmp = tstsample(i-1:i+1,j-1:j+1,k);
tstsample(i,j,k) = nanmean(tmp);
Need help to solve these issues. I found few materials but not exact one
Thank you in advance

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Walter Roberson
Walter Roberson el 1 de Mayo de 2018
Suppose it finds a nan when i=10. Then you would try to access from i-1:i+1 = 9:11. But the maximum for your first dimension is 10.
You could run the code for i=2:9 but you have the general problem that you cannot fix nan that are on the boundary.
  6 comentarios
Shakir Hussain
Shakir Hussain el 3 de Mayo de 2018
Editada: Shakir Hussain el 3 de Mayo de 2018
Codes of Jan`s is dealing well the right and left (columns) corner but did not cover the up and down edge (first and last row), I tired all of his codes.
Walter Roberson
Walter Roberson el 3 de Mayo de 2018
You are mistaken.
In the below, I used Jan's conv2 version, but put on some data creation and some display code to emphasize nans. If you run this code you will see nans on the left highlighted in red. You will not see any nans on the right, but if you look at the code you can see that the display logic is the same so there would be red if the nans existed.
If you examine the values such as comparing x(end-1:end,end-1:end) to X(end-1:end,end-1:end) then you will see that X (the version without nans) has properly calculated X(end,end) based upon the average of the surrounding areas.
if ~exist('x', 'var')
x = randi([0 255], [64 40]);
x(randperm(numel(x),15)) = nan;
x(1,5) = nan; x(end,end) = nan;
image(uint8(x), 'AlphaData', 0+~isnan(x));
set(gca,'color', 'r');
[ny, nx] = find(isnan(x));
hold on
%scatter(nx, ny, 'go')
hold off
X = x;
nanX = isnan(X);
X(nanX) = 0;
mask = [1 1 1; 1 0 1; 1 1 1];
means = conv2(X, mask, 'same') ./ ...
conv2(~nanX, mask, 'same');
X(nanX) = means(nanX);
image(uint8(X), 'AlphaData', 0+~isnan(X));
set(gca,'color', 'r');
[nY, nX] = find(isnan(X));
hold on
%scatter(nX, nY, 'go')
hold off

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Walter Roberson
Walter Roberson el 1 de Mayo de 2018
Editada: Walter Roberson el 2 de Mayo de 2018
  3 comentarios
Walter Roberson
Walter Roberson el 2 de Mayo de 2018
The point was to use one of Jan's solutions posted there.
Walter Roberson
Walter Roberson el 11 de Mayo de 2020
This has no connection to the current Question, and should be posted as its own Question.
a = rgb2gray(a);
You convert rgb image, a to gray, and you replace a with that gray image.
a_g = a( :, :, 2 );
Now you want to access the green plane of the gray image you just created.
Perhaps you should extract the green before converting to gray. Or perhaps you should use a different variable name for the gray image so that you still have the rgb available if you need it.

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