Export 2 Dimension out of a 3 dimensionoal Array

Hi

I hava a 3D Array. Now I like to save the content of the 3d array in n 2d arrays

2dArray = zeros(size(3dArray([1],:,:)));


for z = 1: size(3dArray(:)
    2dArray(z)=3dArray(z,:,:)
end

What am I doing wrong?

Answer 1

[Star Strider]

I am not certain what is the desired result.

Usually, the intent is to separate the ‘pages’ (third dimension) of the array into separate 2D arrays.

Likely the best option for that is —

Array3D = randi(9, 3, 4, 4);
Array3D(:,:,2)                                          % Display Page (Dleete Later)

ans = 3×4

2 8 7 2 8 2 6 4 1 9 3 6

A3dsz = size(Array3D)

A3dsz = 1×3

3 4 4

Arrays2D = mat2cell(Array3D, A3dsz(1), A3dsz(2), ones(1,A3dsz(3)));
Arrays2D{2}                                             % Display Result

ans = 3×4

2 8 7 2 8 2 6 4 1 9 3 6

Make appropriate changes to get the desired result.

.

[Mouse]

yea you are correct, I would like to separate the first page and save it.

All data are saved in the first page.

Now I like to "delete" the page hirarchie and convert the 3d Array into a 2d Array.

[Star Strider]

Please describe the desired result in more detail, preferably with a short, simple example.

[Mouse]

As you see my Dimensions are [1x3883x280]

I would like to exclude the 3883 x 280 and save it in a 2dArray

[Rik]

You simply remove the leading singleton dimensions with squeeze:

data=rand(1,3883,280);
data=squeeze(data);
size(data)

ans = 1×2

3883 280

[Star Strider]

Definitely squeeze in that instance!

@Rik — Thanks!

[Mouse]

thanks Rik

Is there also a possibility to do exact the same thing, only that I have 3 instead of one page.

data=rand(3,3883,280);

now i like to save every page (three at all) in a 2d Array

[Star Strider]

I am not certain what the desired result is.

My initial response demonstrated how to save it in 3 different cell arrays, so to do that, the code changes to —

Array3D = randi(9, 3, 5, 4);
Array3D(2,:,:)                                          % Display Page (Delete Later)

ans = 
ans(:,:,1) =

     9     7     9     5     1


ans(:,:,2) =

     8     1     8     4     9


ans(:,:,3) =

     8     5     1     2     3


ans(:,:,4) =

     4     9     6     3     8

squeeze(Array3D(2,:,:))                                 % Display Page (Delete Later)

ans = 5×4

9 8 8 4 7 1 5 9 9 8 1 6 5 4 2 3 1 9 3 8

A3dsz = size(Array3D)

A3dsz = 1×3

3 5 4

Arrays2D = mat2cell(Array3D, ones(1,A3dsz(1)), A3dsz(2), A3dsz(3));
Arrays2D{2}                                             % Display Result

ans = 
ans(:,:,1) =

     9     7     9     5     1


ans(:,:,2) =

     8     1     8     4     9


ans(:,:,3) =

     8     5     1     2     3


ans(:,:,4) =

     4     9     6     3     8

squeeze(Arrays2D{2})                                      % Display Result

ans = 5×4

9 8 8 4 7 1 5 9 9 8 1 6 5 4 2 3 1 9 3 8

Make appropriate changes to get different results.

I do not recommend using reshape to save it to a single 2D matrix, because that creates significant indexing complications.

.

[Mouse]

data3D=rand(3,3883,280);        %create a 3D array

for i = 1: 3                    %now separate every page of the 3D array into 2D arrays
    oneDataSet = data3D(i,:,:); %cut away a page "slide"
    data_2D=squeeze(oneDataSet);%put away the information that this is a page. Only Information about 2D Array will stay
end

this is my solution to convert a 3 Dimensional Array

[Star Strider]

The code in Comment overwrites ‘data_2D’ in every loop iteration. Only one (the last) 2D matrix created will result.

My code produces 3 separate matrices as cell arrays.

A small addition to it will squeeze all of them as well —

Array3D = randi(9, 3, 5, 4);
Array3D(2,:,:);                                         % Display Page (Delete Later)
squeeze(Array3D(2,:,:))                                 % Display Page (Delete Later)

ans = 5×4

6 9 2 9 7 8 5 8 8 1 8 7 5 7 1 8 6 1 7 6

A3dsz = size(Array3D);
Arrays2D = mat2cell(Array3D, ones(1,A3dsz(1)), A3dsz(2), A3dsz(3));
Arrays2D{2};                                            % Display Result
Arrays2D = cellfun(@squeeze, Arrays2D, 'Unif',0);       % Display Result
Arrays2D{2}

ans = 5×4

6 9 2 9 7 8 5 8 8 1 8 7 5 7 1 8 6 1 7 6

.