indexing error: ()-indexing must appear last in an index expression

Question

Sam 2013-5-10

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评论： Walter Roberson 2016-12-21

Do you know what is wrong with my indexing below? Thanks.

vars = {'Cs' 'beta' 'As' 'TCI' 'TWI' 'hs'}
tmp = cell(size(dem))  % create 20x1 supercell
out = tmp;
tmp2 = size(vars) % create 6x1 subarrays
out2 = zeros(tmp2);
for i=1:numel(dem)
    for j=1:numel(vars)
        *out{i} = out2(:,:,j)(Cs{i}, beta{i}, As{i}, TCI{i}, TWI{i}, hs{i});*
    end
end
Error: ()-indexing must appear last in an index expression.

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Answer 1

the cyclist 2013-5-10

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https://ww2.mathworks.cn/matlabcentral/answers/75349-indexing-error-indexing-must-appear-last-in-an-index-expression#answer_85054

编辑：the cyclist 2013-5-10

In MATLAB you cannot index into an array that you've already indexed into, so you cannot do this

out{i} = out2(:,:,j)(Cs{i}, beta{i}, As{i}, TCI{i}, TWI{i}, hs{i})

But assuming the rest of your code is OK (which I could not check), then you could define a temp variable

 out2_tmp = out2(:,:,j);
 out{i} = out2_tmp(Cs{i}, beta{i}, As{i}, TCI{i}, TWI{i}, hs{i})

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Sam 2013-5-10

Thanks, Cyclist. That made progress yet led to a dreaded error I've hit numerous times but don't fully understand. This is my first attempt at a nested for loop. Can you offer more help? There is no other add'l code, although FYI each 'vars' is a 20x1 cell of n x m arrays.

vars = {'Cs' 'beta' 'As' 'TCI' 'TWI' 'hs'}
tmp = cell(size(dem))
out = tmp;
tmp2 = size(vars)
out2 = zeros(tmp2);
for i=1:numel(dem)
  for j=1:numel(vars)
      out2_tmp = out2(:,:,j);
      out{i} = out2_tmp(Cs{i}, beta{i}, As{i}, TCI{i}, TWI{i}, hs{i});
  end
end

Subscript indices must either be real positive integers or logicals.

the cyclist 2013-5-10

I can't really help debug your code, because it is not self-contained. However, I can give insight into that error.

x = [2 7 6 3];
idx_valid_integers = [1 3 4 2];
idx_valid_logical  = [true true false true];
idx_invalid        = [-1 0];
% Valid indexing
y = x(idx_valid_integers);
% Also valid indexing [using logical indexing]
y = x(idx_valid_logical);
% Not valid indexing (index is neither positive integer nor logical)
y = x(idx_invalid); % This will give you that same error.

The first two ways of indexing work, because I am either telling MATLAB a particular element (by its position) or by applying a logical "mask" to the entire vector.

But the third way does not work. What is the "-1" or "zeroth" element of a vector. It makes no sense.

Somehow, that is what you are doing in your code.

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