How to concatenate the data in each iteration in the same variable?

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M 2023-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/2050152-how-to-concatenate-the-data-in-each-iteration-in-the-same-variable

评论： Walter Roberson 2023-11-21

I am saving the output of the 1st iteration in the images_TRO_pressing , images_TRO_slip, images_TRO_noise, the size of each variabe is 120*120*300

In the other iterations how can I keep adding the data in the same varibales so I end up with size for each of them around 120*120*3600? as well same to the varibale labels_TRO with size 1*900 for one iteration

Note that the third dimension which is the number of matrices varies in each iteration not all iterations give 300.

for i = 1:12      
pressing_labels = find(labels_all_Train1(i).labels == 0);
        slip_labels = find(labels_all_Train1(i).labels == 1);
        noise_labels = find(labels_all_Train1(i).labels == 3);
        minimum = min([length(pressing_labels), length(slip_labels), length(noise_labels)]);
        random_pressing = randsample(pressing_labels, minimum);
        random_slip = randsample(slip_labels, minimum);
        random_noise = randsample(noise_labels, minimum);
        images_TRO_pressing = HM_all_Train1(i).TRO_heatmap(:, :, random_pressing);
        images_TRO_slip =  HM_all_Train1(i).TRO_heatmap(:, :, random_slip);
        images_TRO_noise = HM_all_Train1(i).TRO_heatmap(:, :, random_noise);
        labels_TRO = [labels_all_Train1(i).labels(random_pressing), labels_all_Train1(i).labels(random_slip), labels_all_Train1(i).labels(random_noise)];
    end

16 个评论
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Dyuman Joshi 2023-11-21

编辑：Dyuman Joshi 2023-11-21

在 MATLAB Online 中打开

"Could you please provide me with example because I tried it but it keeps only return the last iteration I dont know what is the error"

Try this -

n=12;
labels_TRO = cell(n,1);
for i = 1:n
        %Allocate data which needs to be accessed frequently to a variable 
        arr = labels_all_Train1(i).labels;
        
        pressing_labels = nnz(arr == 0);
        slip_labels = nnz(arr == 1);
        noise_labels = nnz(arr == 3);
        
        minimum = min([pressing_labels, slip_labels, noise_labels]);
        random_pressing = randperm(pressing_labels, minimum);
        random_slip = randperm(slip_labels, minimum);
        random_noise = randperm(noise_labels, minimum);
        images_TRO_pressing = HM_all_Train1(i).TRO_heatmap(:, :, random_pressing);
        images_TRO_slip =  HM_all_Train1(i).TRO_heatmap(:, :, random_slip);
        images_TRO_noise = HM_all_Train1(i).TRO_heatmap(:, :, random_noise);
        labels_TRO{i} = [arr(random_pressing), arr(random_slip), arr(random_noise)];
end

See Preallocation for more info.

"Can you please show me how can I use it to take a random sample with a certain number of samples from a vector, I didnt find this in the documentation"

%4 random numbers from 1 to 10
randsample(10,4)
ans = 4×1
     9
     3
     6
     5
randperm(10,4)
ans = 1×4
     6     7     9     1

M 2023-11-21

编辑：M 2023-11-21

@Walter Roberson Thanks a lot, this is worked and thanks for @Dyuman Joshi

but I am wondering why the logical indexing instead of "find" didnt work, any suggestion please?

Walter Roberson 2023-11-21

You have not been clear as to what your code is, or what your desired outcomes are.

If you are trying to find N locations each of which correspond to a particular arr value, then you have a few possibilities:

do NOT just take arr(LOGICAL MASK) since you already know what the arr values are at those locations because that is how you chose the locations
taking a random sub-sampling of a logical mask would get you are random number of elements selected, and would not tell you where they were selected from
using find() to locate the elements and taking a random selection from those indices works fine if what you want to know is the locations
You could create a vector 1:numel(arr) and index that vector at a logical matrix such as arr==0 ... but you would effectively just have duplicated the work of find() less efficiently

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