How can I count the number of times a value occurs

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Gina Carts
Gina Carts 2020-2-6
评论： Rik 2020-2-8
Hi there,
I have a 3D array (mask) with the numbers 0 background, 1, 2, 3 and 4. The numbers 1,2,3 and 4 correspond to particular regions.
I want to count how many regions in my 3D mask have the number 1,2,3, or 4.
Does anyone know how to do this?

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Rik
Rik 2020-2-6
编辑：Rik 2020-2-7
You can use bwlabeln to label all your non-zero regions. then you can loop through each of the labeled regions to determine which number they have. With that, you essentially have the result you need.
If you don't have the image processing toolbox, let me know, because I have an alternative that doesn't require any toolbox.
Edit: added the example below.
%generate example data where max(L(:)) returns about 30
IM=randi(300000,100,100,100);
IM(IM>10)=0;
[L,n_regions]=bwlabeln(IM>0);
counts=zeros(1,max(IM(:)));
for n=1:n_regions
ind=find(L==n,1);
field_val=IM(ind);
counts(field_val)=counts(field_val)+1;
end
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Gina Carts
Gina Carts 2020-2-7
I think I see how it works. When I print the counts I got the following:
counts =
4 5 4 2 2 4 1 5 1 5
That means I have 4 regions with number 1, 5 regions with number 2 etc. Am I correct?
Rik
Rik 2020-2-8
Yes, that is the idea. There might be more efficient ways to get to this vector, but this is what I could come up with.

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