How do i create a 3D Matrix?

Question

Robert 2014-10-2

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编辑： Stephen23 2020-3-9

采纳的回答： Stephen23

I have 12 workspace files all 35x43. I want to make them into one 35x43x12 matrix. What is the best way to do so?

Thanks in advance for any help!

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Robert 2014-10-2

Sorry, I'm very much a matlab newbie. By Workspace files i mean 12 individual matrices. Loops are a little beyond me still. Could you provide an example code?

Thanks for taking the time to assist me

Stephen23 2014-10-2

编辑：Stephen23 2014-10-2

How do you generate these matrices?

(I know it might seem unrelated, but trust me...)

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Answer 1

Stephen23 2014-10-2

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编辑：Stephen23 2014-10-2

在 MATLAB Online 中打开

If these matrices are existing variables in your workspace, you can concatenate them on the dimension of your choice:

>> A = [1,2;3,4];
>> B = [5,6;7,8];
>> C = [9,10;11,12];
>> Z = cat(3,A,B,C)

Note that in MATLAB it is often easier, faster and neater to keep all data together, and use vectorization to perform operations on the array data In this case, this might mean keeping all of the arrays in one cell array:

>> D = {first_matrix,second_matrix,...};
>> Z = cat(3,D{:})

OR it might even be better to define the data in one array to start with, rather than in twelve separate matrices. Good data planning in MATLAB makes a world of difference to how easy (and readable!) your code will be.

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Gaia Gbola 2020-3-9

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Hello,

I am trying to stack a series of png images, by using a for loop. Could I get help? I keep getting an error by using this code:

clc;clear all;
%A = [imread('frame-3.png') ; imread('frame-4.png');];
for i=1:2456
    
D = {imread('frame-',(i),'.png')};
Z = cat(3,D{:})
end
imshow(Z)

Stephen23 2020-3-9

编辑：Stephen23 2020-3-9

在 MATLAB Online 中打开

@Gaia Gbola : try something like this:

P = 'absolute/relative path to where the files are saved';
N = 2456;
C = cell(1,N);
for k = 1:N
    F = sprintf('frame-%u.png',k);
    C{K} = imread(fullfile(P,F));
end
A = cat(4,C{:}) % pick a suitable dimension

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Answer 2

Stephen23 2014-10-2

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https://ww2.mathworks.cn/matlabcentral/answers/157040-how-do-i-create-a-3d-matrix#answer_153571

编辑：Stephen23 2014-10-2

A typical way to read multiple files in MATLAB would be:

Preallocate an array of zeros , using the optional argument to make it size 35x43x12.
Use a loop to read the data from each file, and allocate the values into the array using some indexing . Note that MATLAB indexing is one-based, and is row-major: X(row,col,3rdDim,4thDim,...)