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

1 次查看（过去 30 天）

lit 2023-8-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2007062-how-can-i-select-two-out-of-6-points-for-every-page-without-loops

编辑： Bruno Luong 2023-8-15

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 个评论
显示 6更早的评论隐藏 6更早的评论

Bruno Luong 2023-8-11

编辑：Bruno Luong 2023-8-11

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 2023-8-11

编辑：lit 2023-8-11

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.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Jan 2023-8-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2007062-how-can-i-select-two-out-of-6-points-for-every-page-without-loops#answer_1285952

在 MATLAB Online 中打开

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 个评论
显示 4更早的评论隐藏 4更早的评论

lit 2023-8-15

编辑：lit 2023-8-15

在 MATLAB Online 中打开

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 2023-8-15

编辑：Bruno Luong 2023-8-15

在 MATLAB Online 中打开

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, [])