How to extract data from a 3D Array?

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Simon Schirk
Simon Schirk 2024-4-18
回答： Dyuman Joshi 2024-4-18
I have a large (500x5x79039) 3D array, which is mostly filled with zeros. Now I want to extract the slices with content into a smaller array and save them. I’ve already tried the solution from this Article, but then I get the same page repeated multiple times, resulting in too many entries and duplicates.
Ideally, I would like to extract the pages exactly as they were saved, provided there is data on those pages.
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Harald
Harald 2024-4-18
Jonas inquired about the direction of indexing. In other words, you can get
a) a n x 5 x 79039 array with n < 500
b) a 500 x n x 79039 array with n < 5
c) a 500 x 5 x n array with n < 79039
Each can be done, but it would be great to know which of the three you are looking for.
Simon Schirk
Simon Schirk 2024-4-18
Sorry, my bad. I'm looking for c). The Data I'm looking for should be displayed as 500 x 5 x n, like the pages in my existing array.

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回答（1 个）

Dyuman Joshi
Dyuman Joshi 2024-4-18
Ran in:
Use logical indexing -
%Sample data
p = 5;
q = 6;
r = 4;
y = rand(p,q,r)-1;
y(:, :, [2 r+1]) = zeros(p,q,2)
y =
y(:,:,1) = -0.7285 -0.6881 -0.6747 -0.3796 -0.1672 -0.6574 -0.9762 -0.6068 -0.9793 -0.0795 -0.9972 -0.5266 -0.7477 -0.1073 -0.9397 -0.5630 -0.9243 -0.7642 -0.2448 -0.1465 -0.7908 -0.8282 -0.3473 -0.0134 -0.3137 -0.4403 -0.8926 -0.5689 -0.2770 -0.4045 y(:,:,2) = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 y(:,:,3) = -0.0481 -0.3703 -0.8937 -0.2620 -0.6424 -0.1590 -0.3590 -0.7458 -0.8042 -0.6762 -0.5639 -0.4337 -0.4247 -0.3759 -0.6399 -0.7271 -0.9687 -0.0107 -0.3895 -0.5470 -0.2762 -0.8224 -0.4897 -0.7164 -0.5377 -0.7156 -0.8387 -0.6348 -0.3393 -0.1025 y(:,:,4) = -0.7409 -0.3158 -0.9468 -0.7263 -0.4370 -0.7029 -0.3200 -0.8704 -0.2631 -0.8824 -0.4113 -0.4293 -0.5657 -0.7926 -0.9319 -0.6440 -0.1914 -0.1186 -0.0940 -0.8801 -0.3449 -0.3131 -0.0717 -0.8211 -0.6848 -0.8336 -0.2107 -0.4389 -0.7302 -0.3056 y(:,:,5) = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
%Check if there is any non-zero element in a page
idx = any(y, [1 2])
idx = 1x1x5 logical array
idx(:,:,1) = 1 idx(:,:,2) = 0 idx(:,:,3) = 1 idx(:,:,4) = 1 idx(:,:,5) = 0
%Use the (logical) index to get the corresponding data
out = y(:, :, idx)
out =
out(:,:,1) = -0.7285 -0.6881 -0.6747 -0.3796 -0.1672 -0.6574 -0.9762 -0.6068 -0.9793 -0.0795 -0.9972 -0.5266 -0.7477 -0.1073 -0.9397 -0.5630 -0.9243 -0.7642 -0.2448 -0.1465 -0.7908 -0.8282 -0.3473 -0.0134 -0.3137 -0.4403 -0.8926 -0.5689 -0.2770 -0.4045 out(:,:,2) = -0.0481 -0.3703 -0.8937 -0.2620 -0.6424 -0.1590 -0.3590 -0.7458 -0.8042 -0.6762 -0.5639 -0.4337 -0.4247 -0.3759 -0.6399 -0.7271 -0.9687 -0.0107 -0.3895 -0.5470 -0.2762 -0.8224 -0.4897 -0.7164 -0.5377 -0.7156 -0.8387 -0.6348 -0.3393 -0.1025 out(:,:,3) = -0.7409 -0.3158 -0.9468 -0.7263 -0.4370 -0.7029 -0.3200 -0.8704 -0.2631 -0.8824 -0.4113 -0.4293 -0.5657 -0.7926 -0.9319 -0.6440 -0.1914 -0.1186 -0.0940 -0.8801 -0.3449 -0.3131 -0.0717 -0.8211 -0.6848 -0.8336 -0.2107 -0.4389 -0.7302 -0.3056

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