save values of 2D matrix into a multidimensional matrix

2 次查看（过去 30 天）

显示更早的评论

Mikel 2022-9-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1812430-save-values-of-2d-matrix-into-a-multidimensional-matrix

编辑： J. Alex Lee 2022-9-28

在 MATLAB Online 中打开

Hello,

I have a for loop where a I generates two new points in every loop for my 2xn matrix where n=15001.

I want to save values from this matrix that meets 4 conditions into m different 2 x k matrixes (sizes are not the same for each matrix) where m=221. Maybe I need to use cells but I'm having issues when creating the nested for loop for this operation, I can not achieve what I'm aiming for, I need help please. Here my code:

for ind2=2:15001
%some previous code that generates points for x1x2 matrix (its long)
% save values of x1d x2d
    x1x2(:,ind2)=[x1d(1,ind2);x2d(ind2)];
    for indX1=1:16
        for indX2=1:12
                if (x1x2(1,ind2)>X1(indX1) && x1x2(1,ind2)<X1(indX1+1) && x1x2(2,ind2)>X2(indX2) && x1x2(2,ind2)<X2(indX2+1))
                    %Here my issue, Im not able to create this
                    %multidiemnsional matrix
                    ROIx1x2(:,count,m)= x1x2(:,ind2);
                    
                    F(count,1,m)= fintd(:,ind2);
    
                    count=count +1;
                end
        end
    end
end

7 个评论
显示 5更早的评论隐藏 5更早的评论

Mikel 2022-9-27

在 MATLAB Online 中打开

points.mat

Hello, sorry for not giving all the information you needed. I attached a small example with my real data.

Dyuman Joshi - what I mean is that the matrix that I'm creating is not containing the expected output. I'm getting a 2x15000x221 matrix but, it should be something like, 2x (different sizes) x 221. I understand that somehow matlab is filling this arrays with 0 values but all I want to have is only the values that meets the conditions.

Jan - x1x2 is preallocated but ROIx1x2 and F are not as their sizes change. I know is expensive but I dont know how can I manage this, I was thinking about cells, but not sure.

Benjamin Thompson attached an example code with my real data.

%% INIT
clear variables;
close all;
clc;
%%
%ROIx1x2 and F are not pre-allocated as the size changes.
load('points.mat', 'x1x2','X1','X2','PDLUT','fintd');
m=numel(PDLUT);
count=1;
for ind2=2:15001
    for indX1=1:16
        for indX2=1:12
                if (x1x2(1,ind2)>X1(indX1) && x1x2(1,ind2)<X1(indX1+1) && x1x2(2,ind2)>X2(indX2) && x1x2(2,ind2)<X2(indX2+1))
                    %Here my issue, Im not able to create this
                    %multidiemnsional matrix
                    %my output 2x15000x221
                    
                    %expected output 2x(different sizes)x221
                    ROIx1x2(:,count,m)= x1x2(:,ind2);
                    
                    F(1,count,m)= fintd(:,ind2);
    
                    count=count +1;
                end
        end
    end
end

Jan 2022-9-27

编辑：Jan 2022-9-27

在 MATLAB Online 中打开

@Mikel: You can pre-allocate arrays with a maximum size and crop them afterwards:

x  = zeros(1e6, 1);
ix = 0;
for k = 1:1e6
   if rand > 0.5
       ix    = ix + 1;
       x(ix) = 27;
   end
end
x = x(1:ix);

This reserves 8 MB. Without an preallocation, a new array is created in each iteration with matching condition, so you allocate about sum(1:0.5e6)*8 Byte, which is 1 TB. Although most of this memory is released soon, allocating it is expensive.

You can accelerate the code:

for ind2=2:15001
    for indX1=1:16
        for indX2=1:12
             if (x1x2(1,ind2)>X1(indX1) && x1x2(1,ind2)<X1(indX1+1) && x1x2(2,ind2)>X2(indX2) && x1x2(2,ind2)<X2(indX2+1))
              %  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If this condition is FALSE, running the inner loop over indX2 is a waste of time. Better:

for ind2=2:15001
    for indX1=1:16
        if x1x2(1,ind2) > X1(indX1) && x1x2(1,ind2) < X1(indX1+1)
           for indX2=1:12
              if x1x2(2,ind2)>X2(indX2) && x1x2(2,ind2)<X2(indX2+1)

Mikel 2022-9-28

Thank you! this is what I was looking for

J. Alex Lee 2022-9-28

编辑：J. Alex Lee 2022-9-28

在 MATLAB Online 中打开

The value of m is static, is it supposed to be something like sub2ind(size(PDLUT),indX1,indX2) or something?

I wonder if what you are looking for ultimately is something like a 2D histogram, or you can extract what you need from it:

histogram2(x1x2(1,:),x1x2(2,:),X1,X2)
[N,XEDGES,YEDGES,BINX,BINY] = histcounts2(x1x2(1,:),x1x2(2,:),X1,X2);

请先登录，再进行评论。

请先登录，再回答此问题。

回答（0 个）

请先登录，再回答此问题。

类别

MATLAB Mathematics Graph and Network Algorithms Construction Directed Graphs

在 Help Center 和 File Exchange 中查找有关 Directed Graphs 的更多信息

产品

MATLAB

版本

R2021b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by

save values of 2D matrix into a multidimensional matrix

7 个评论
显示 5更早的评论隐藏 5更早的评论

回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

save values of 2D matrix into a multidimensional matrix

7 个评论 显示 5更早的评论隐藏 5更早的评论

回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

WeChat

7 个评论
显示 5更早的评论隐藏 5更早的评论