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How can I select two out of 6 points for every page without loops?

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lit
lit am 10 Aug. 2023
Bearbeitet: Bruno Luong am 15 Aug. 2023
I am trying to select two out of 6 points in an array whose size is 6x3xn. These two points are not in the same row on each page as I am trying to select those two of the six points that meet a certain condition. Let's assume that condition is that every coordinate is between 0 and 30.
Is there away to do this without loops?
  8 Kommentare
Bruno Luong
Bruno Luong am 11 Aug. 2023
Bearbeitet: Bruno Luong am 11 Aug. 2023
So the number of pages that satisfies that (exactly 2 rows are find) would reduce. And you might keep track of which of those are not discarded, which are.
Your discription "... for every page" "...on each page" are missleading if not wrong.
lit
lit am 11 Aug. 2023
Bearbeitet: lit am 11 Aug. 2023
I'm sorry, I only realized that I don't actually need the pages where not exactly two points are found after writing the question.

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Akzeptierte Antwort

Jan
Jan am 10 Aug. 2023
n = 2;
X = randi(40, 6, 3, n)
X =
X(:,:,1) = 25 18 19 19 23 18 26 5 7 15 39 10 22 35 10 26 35 23 X(:,:,2) = 35 22 6 25 29 2 5 39 5 34 33 36 32 14 17 5 22 33
mask = all(X >= 0 & X <= 30, 2)
mask = 6×1×2 logical array
mask(:,:,1) = 1 1 1 0 0 0 mask(:,:,2) = 0 1 0 0 0 0
Y = reshape(X(cat(2, mask, mask, mask)), [], 3)
Y = 4×3
25 23 7 19 5 25 26 19 29 18 18 2
  6 Kommentare
lit
lit am 15 Aug. 2023
Bearbeitet: lit am 15 Aug. 2023
my code now looks like this
X = randi(40,6,3,4)
X =
X(:,:,1) = 12 17 1 32 6 13 35 9 16 2 24 17 20 35 34 10 16 30 X(:,:,2) = 10 3 40 5 30 35 27 22 40 3 35 11 33 29 21 31 7 7 X(:,:,3) = 4 25 17 25 25 8 2 34 4 32 12 25 36 20 7 19 25 32 X(:,:,4) = 10 26 3 33 15 27 19 4 34 2 31 27 30 19 25 12 19 8
mask = all(X>=0 & X<=30,2);
mask(:,:,sum(mask,1)~=2) = 0;
X = permute(X, [2 1 3]);
mask = permute(mask,[2 1 3])
mask = 1×6×4 logical array
mask(:,:,1) = 0 0 0 0 0 0 mask(:,:,2) = 0 0 0 0 0 0 mask(:,:,3) = 1 1 0 0 0 0 mask(:,:,4) = 0 0 0 0 0 0
X = reshape(X(cat(1,mask, mask, mask)),3,[])'
X = 2×3
4 25 17 25 25 8
So now 2 points only on pages where exactly 2 points meet the condition are selected
Sorry in case I have confused you
Bruno Luong
Bruno Luong am 15 Aug. 2023
Bearbeitet: Bruno Luong am 15 Aug. 2023
OK this looks correct. But I don't think you need permute and transpose at all. It seems like a side effect of your though trying to fix Jan's coden but that is not relevant.
n = 4;
nsolperpage = 2;
X = randi(40, [6, 3, n])
mask = all(X >= 0 & X <= 30, 2);
keep = sum(mask,1) == nsolperpage;
extractpages = find(keep)
mask(:,:,~keep) = false;
Y = reshape(X([mask, mask, mask]), nsolperpage, 3, [])

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Bruno Luong
Bruno Luong am 15 Aug. 2023
n = 4;
nsolperpage = 2;
X = randi(40, [6, 3, n])
mask = all(X >= 0 & X <= 30, 2);
[~,p] = find(reshape(mask, [], n));
count = accumarray(p, 1, [n 1]);
keep = count == nsolperpage;
extractpages = find(keep)
mask(:,:,~keep) = false;
Y = reshape(X([mask, mask, mask]), nsolperpage, 3, [])

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