Unable to perform assignment because brace indexing is not supported for variables of this type.

Dear Matlab Community,

in a loop I am trying to write variables into a cell.

For variable sub_matrix it works, however for sub_matrix_idx it does not.

The error message:Unable to perform assignment because brace indexing is not supported for variables of this type.

The former are pixel values of an image in double format, the latter returns the position of these pixels on the image (also double, please see attached).

Any suggestions are appreciated

best

lg

[Matt J]

We need to see a demonstration of what you did, which you can provide using the Run button

[Levente Gellért]

Dear MAtt J please find the code with the working indexing only.

clear all
I=imread ('pout.tif');
I=im2double(I);
imshow(I);
h = drawfreehand; 
bw = createMask(h);
I(bw==1)=NaN;
[r,c] = size(I);
sz=[r c];
roi_x=9;
roi_y=9;
index=1;
sub_matrices=cell(1, 10);
for i=1:1000
    startpoint=(randi(numel(I)));
    [row,col] = ind2sub(sz,startpoint);
    if col+roi_x>c
        col=col-(roi_x+1);
    end
    if row+roi_y>r
        row=row-(roi_y+1);
    end
    sub_matrix = I(row:(row+roi_y),col:(col+roi_x));
    I_idx=1:numel(I);
    I_idx=reshape (I_idx,[291,240]);
    sub_matrix_idx=I_idx(row:(row+roi_y),col:(col+roi_x));
    if anynan(sub_matrix)==1
        index = index;
        continue
    else
        index=index+1;
    end
    roi = images.roi.Rectangle(gca,'Position',[col,row,roi_x,roi_y]);
    if index == 11
        sub_matrices{1, index-1}=sub_matrix;
        break
    end
    sub_matrices{1, index-1}=sub_matrix;
end 

[Walter Roberson]

Which line is the error occurring on?

[Levente Gellért]

Dear Walter Robertson,

if I try to write sub_matrix_idx to a cell like I do witH "sub_matrices{1, index-1}=sub_matrix;"

I got the error message.

thanks

lg

[Image Analyst]

What does this show

whos sub_matrix
whos sub_matrices

I ran your code, drew a region, and it finished with no error. I tried several time.

But what are you trying to do? In words, rather than code. There might be a better way.

I attach some demos that might help.

Answer 1

[Walter Roberson]

Your posted code has no indexed assignments to sub_matrix_idx so you need to post the code that you actually used.

    I_idx=1:numel(I);

Numeric.

    I_idx=reshape (I_idx,[291,240]);

reshape() of a numeric is numeric.

    sub_matrix_idx=I_idx(row:(row+roi_y),col:(col+roi_x));

() indexing of something numeric gives a numeric result.

So sub_matrix_idx is numeric, not cell. Using {} indexing to try to assign into it would be a mistake.

You could convert sub_matrix_idx into a cell using

    sub_matrix_idx = num2cell(sub_matrix_idx);

but if you do, then watch out for your

    if anynan(sub_matrix)==1

statement, as anynan() cannot operate on cell arrays.

Answer 2

[Ryan Baird]

It looks like sub_matrix is a matrix rather than a cell array, so it should be accessed with parenthesis:

sub_matrix(i, j) = ...

and not with braces:

sub_matrix{i, j} = ...

Answer 3

[Levente Gellért]

Dear Walter Roberson Dear Ryan Baird,

thanks for the helpful comments, now everything runs well.

Best

lg