MATLAB: Accessing the deeper components of a cell array

cell arraysindexing

Supposing I have an Nx1 cell array, in which each cell contains a 3×1 vector – how do I extract the third component of each vector in the cell array?

i.e. I need something like: cellarray{:,1}(3,1)

which doesn't work.

I realize this is basic but I've been messing around for a while and couldn't come up with a solution

Best Answer

You don't have a choice but use a loop or cellfun (which is a loop in effect):

cellfun(@(v) v(3), yourcellarray)

will return a vector of the 3rd element of each cell.

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MATLAB: Connect bwlabeled components

Using bwconncomp on a three dimensional image will group them in 3d. You'll have to call it on each individual slice to see how many objects per slice there are:

sliceObjs = zeros(size(stack,3),1);
for ii = 1:size(stack,3)
 CC = bwconncomp(stack(:,:,ii));
 sliceObjs(ii) = CC.NumObjects;
end

EDIT This is a script, with the engine completely generalized and ready to go. I saved you above image; cropped it and translated it for visualization error checking purposes. The translation was done using my function FEX:imtranslate

%%Data and stuff
I = imread('ans627.png'); %your image
I = I(35:276,86:381,1)==255; %keep relevant part; convert to binary
I(:,:,2) = imtranslate(I,[10 -14]); %artificially translate for testing
I(5:11,270:275,2) = true;  %add an eleventh object with no friends
szI = size(I); 
Ds = cell(szI(3)-1); %preallocate place to store stuff
CCold = bwconncomp(I(:,:,1));  %cc of first slice
RPold = regionprops(CCold,'centroid');
centsA = vertcat(RPold(:).Centroid); %extract centroids
for ii = 1:(szI(3)-1)
  CCnew = bwconncomp(I(:,:,ii+1));  %cc of next slice
  RPnew = regionprops(CCnew,'centroid');
  centsB = vertcat(RPnew(:).Centroid);
    dim = 2; %which dimension will control in the bsxfun expression?
    if CCold.NumObjects>CCnew.NumObjects
        dim = 1;
    end    
    %Engine:
    xyDiff = bsxfun(@(x,y)abs(x-y),reshape(centsA,[],1,2),reshape(centsB,1,[],2)); %Centroids distances in each dimension
    [~,idx] = min(hypot(xyDiff(:,:,1),xyDiff(:,:,2)),[],dim);
    if dim==2;
        displacements = centsB(idx,:)-centsA;
        H = quiver(centsA(:,1),centsA(:,2),displacements(:,1),displacements(:,2));
    else
        displacements = centsB-centsA(idx,:);
        H = quiver(centsB(:,1),centsB(:,2),displacements(:,1),displacements(:,2));
    end
    RPold = RPnew; %get ready to move on
    CCold = CCnew; 
    centsA = centsB;
    Ds{ii} = displacements;  %can store other stuff too.
end
%SCd 06/27/2011

If you now look at displacements, you'll see that the artificial translation was recovered. I didn't place a threshold on distance - just used the minimum one. This could be added easily enough. (replace objects without a match to nan to maintain order)

MATLAB: Delete empty [] {1×7 cell} {1×2 cell}

z(cellfun('isempty',z))=[]

Best Answer

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MATLAB: Connect bwlabeled components

MATLAB: Delete empty [] {1×7 cell} {1×2 cell}

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