How can I delete the rows and columns of a 3D matrix? I tried to use the following Px((1:(Col​​umn1-1)),​:​,i)=[] but I am getting this error "A null assignment can have only one non-colon index." How can I correct it?

clear all
clc
dicomlist = dir(fullfile(pwd,'SER_7_Dicoms','*.dcm'));
for cnt = 1 : numel(dicomlist)
   I{cnt} = dicomread(fullfile(pwd,'SER_7_Dicoms',dicomlist(cnt).name));
%    Each{cnt} = char(dicomlist(cnt).name)
%    %info = dicominfo('MR03318.dcm');
%    %dicominfo(dicomlist(cnt).name)
end

for cnt = 1 : numel(dicomlist)
   info{cnt} = dicominfo(fullfile(pwd,'SER_7_Dicoms',dicomlist(cnt).name));

end

for i = 1:length(info)
    Rows(i) = double(info{1,i}.Rows);
    Columns(i) = double(info{1,i}.Columns);
    Pixel_Spacing(:,i) = double(info{1,i}.PixelSpacing); %in mm/pixel
    Pixel_Spacing_x(:,i) = double(info{1,i}.PixelSpacing(1));
    Pixel_Spacing_y(:,i) = double(info{1,i}.PixelSpacing(2));
    Patient_Position(:,i) = double(info{1,i}.ImagePositionPatient);
    Sx(:,i) = double(info{1,i}.ImagePositionPatient(1));
    Sy(:,i) = double(info{1,i}.ImagePositionPatient(2));
    Sz(:,i) = double(info{1,i}.ImagePositionPatient(3));
    Image_Orientation(:,i) = double(info{1,i}.ImageOrientationPatient);
    F12(:,i) = double(Image_Orientation(4,i));
    F22(:,i) = double(Image_Orientation(5,i));
    F32(:,i) = double(Image_Orientation(6,i));
    F11(:,i) = double(Image_Orientation(1,i));
    F21(:,i) = double(Image_Orientation(2,i));
    F31(:,i) = double(Image_Orientation(3,i));
    F1(:,i) = [F11(:,i) F21(:,i) F31(:,i)];
    F2(:,i) = [F12(:,i) F22(:,i) F32(:,i)];
    n(:,i) = cross(F1(:,i),F2(:,i))%vector normal to the plane
    magnitude(:,i) = sqrt(n(1,i)^2+n(2,i)^2+n(3,i)^2);
    n_normalized(:,i) = n(:,i)/magnitude(:,i);

      V1 = 202.0;
      V2 = 220.0;
      H1 = 80.0;
      H2 = 120.0;

      Row1(:,i) = round(V1/Pixel_Spacing_y(:,i));
      Row2(:,i) = round(V2/Pixel_Spacing_y(:,i));
      Column1(:,i) = round(H1/Pixel_Spacing_x(:,i));
      Column2(:,i) = round(H2/Pixel_Spacing_x(:,i));
      Delta_r_ROI(:,i) = double(Pixel_Spacing_x(:,i));
      Delta_c_ROI(:,i) = double(Pixel_Spacing_y(:,i));

      %fileID(i) = fopen(sprintf('New%d.dat',i),'w');
      A(:,:,i) = [(F11(:,i)*Delta_r_ROI(:,i)) (F12(:,i)*Delta_c_ROI(:,i)) 0 Sx(:,i); F21(:,i)*Delta_r_ROI(:,i) F22(:,i)*Delta_c_ROI(:,i) 0 Sy(:,i); F31(:,i)*Delta_r_ROI(:,i) F32(:,i)*Delta_c_ROI(:,i) 0 Sz(:,i);0 0 0 1];
      subImage(:,:,i) = I{1,i}(Row1(:,i):Row2(:,i), Column1(:,i):Column2(:,i));
      %figure(i), imshow(subImage(:,:))

      for r = (Row1(:,i)):(Row2(:,i))
          for c = Column1(:,i):Column2(:,i)
              B(:,i) = [r;c;0.0;1.0];
              P(:,:,i) = A(:,:,i)*B(:,i);
              Px(c,r,i)=P(1,:,i);
              Py(c,r,i)=P(2,:,i);
              Pz(c,r,i)=P(3,:,i);
              %disp([r c])
          end 
      end

      Px((1:(Column1-1)),:,i)=[];
      Py(1:(Column1-1),:,i)=[];
      Pz(1:(Column1-1),:,i)=[];

      Px(:,1:(Row1-1),i)=[];
      Py(:,1:(Row1-1),i)=[];
      Pz(:,1:(Row1-1),i)=[];

Answer 1

[the cyclist]

Suppose you have the 2-dimensional matrix

A = [1 4 7;
     2 5 8;
     3 6 9]

and try the command

A(3,3) = []

You are telling MATLAB to remove the 9. But that makes no sense. What is left is not a matrix. You could insert some other value there, such as

A(3,3) = NaN

but you cannot just remove it.

You are trying to do the same thing in your array.

[HH0825]

It works for a 2D array for instance:Px((1:(Column1-1),:). However when I have the loop that introduces the index i my Px matrix becomes 3D and therefore the syntax does not work anymore. When I use Px((1:(Column1-1)),:,i)=NaN it works. But I don't want to have NaN in my data output.

Answer 2

[Image Analyst]

You have to erase a whole plane, not just some columns.

[HH0825]

so how can I do it?

[Walter Roberson]

Px((1:(Column1-1)),:,:)=[]

You might wanting to loop over the third dimension, but MATLAB does not know that Column1 is not going to change on the other panes and so does not know that "eventually" it would not be a "ragged array". And if you know that Column1 is not going to change then just do it all at once like the above.