Simple For Loop To Find Indices

Question

Melissa 2015-4-20

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编辑： Guillaume 2015-4-20

Hello.

I have a question about a simple for loop. I have an original latlon set of about 500x1 unique coordinates. I have a subset of that latlon set in which I would like to find the indices for. So I have created a for loop to try to find it.

   indices = zeros(length(subset),1); %create matrix of zeros to fill
      for ii=1:length(subset);
          indices(ii) = find(original==subset(ii));
      end

But I keep getting: Subscripted assignment dimension mismatch. What am I doing wrong? In the end I want a matrix the size of the subset to indicate which indices are correlated to my latlon subset in relation to my original latlon.

Thank you,

Melissa

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Answer 1

Guillaume 2015-4-20

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编辑：Guillaume 2015-4-20

在 MATLAB Online 中打开

The only way you can get this error with the code you've presented is if is find returns strictly less or more than one element, that is either the element of your subset is not found, or it is found more than once (i.e. your original array is not unique).

In any case, the loop is not needed there are set functions already present in matlab to do what you want. In your case, it's simply:

[~, indices] = ismember(subset, original)

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Answer 2

Hikaru 2015-4-20

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编辑：Hikaru 2015-4-20

Are your variables stored as double, or cells?

edit: I'm sorry. I made a mistake and I removed the incorrect statement.

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Melissa 2015-4-20

Hi Hikaru,

They're stored as double. So how should I modify it so that I am not comparing a whole vector to one value? Do I add another loop inside of that loop?

Hikaru 2015-4-20

在 MATLAB Online 中打开

I tried your code using a smaller sized variables,

original = [60; 40; 100; 120];
subset = [120; 40; 60];
indices = zeros(length(subset),1);
for ii=1:length(subset);
    indices(ii) = find(original==subset(ii))
end

and it works okay as long as the values in subset can also be found in the original vector.

I'm not sure why you got that error without looking at the sample matrix, but have you check if there are same values in the original vector?

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