# How to concatenate 3D matrixes effectively/fast

5 vues (au cours des 30 derniers jours)
Hugo le 21 Fév 2022
Commenté : DGM le 21 Fév 2022
Hi,
I have 5 matrixes, named M1,M2,M3,M4 and M5. They are all 48*1000*C, with C different in each case. I would like to concatenate M1 to M5, in dimension 3. I have written the following code:
ntables=40
nlines=1000
ncolumns1=10
ncolumns2=15
ncolumns3=20
ncolumns4=25
ncolumns5=30
M1=zeros(ntables, nlines, ncolumns1);
M2=zeros(ntables, nlines, ncolumns1);
M3=zeros(ntables, nlines, ncolumns2);
M4=zeros(ntables, nlines, ncolumns3);
M5=zeros(ntables, nlines, ncolumns4);
for i=1:nlines
dataC1(:,i,:)=cat(3,M1(:,i,:),M2(:,i,:))
dataC2(:,i,:)=cat(3,dataC1(:,i,:),M3(:,i,:))
dataC3(:,i,:)=cat(3,dataC2(:,i,:),M4(:,i,:))
dataC4(:,i,:)=cat(3,dataC3(:,i,:),M5(:,i,:))
end
The problem is that the code above is taking very long to run, like it is running for more than 1 week. Is there a faster and easier way to code this?
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### Réponse acceptée

DGM le 21 Fév 2022
Modifié(e) : DGM le 21 Fév 2022
... why not just concatenate them?
ntables=10
nlines=10
ncolumns1=10
ncolumns2=15
ncolumns3=20
ncolumns4=25
ncolumns5=30
M1=zeros(ntables, nlines, ncolumns1);
M2=zeros(ntables, nlines, ncolumns2);
M3=zeros(ntables, nlines, ncolumns3);
M4=zeros(ntables, nlines, ncolumns4);
M5=zeros(ntables, nlines, ncolumns5);
dataC = cat(3,M1,M2,M3,M4,M5);
If there's no need for M1, etc, then there's no need to concatenate at all.
ntables = 10
nlines = 10
ncolumns = [10 15 20 25 30];
dataC = zeros(ntables,nlines,sum(ncolumns));
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### Plus de réponses (1)

Hugo le 21 Fév 2022
Hi,
Thank you for your reply. However, I am not trying to concatenate null matrixes. Instead, I am pre-allocating it. The matrixes M1....M5 are filled with values, not only 0.
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Walter Roberson le 21 Fév 2022
Modifié(e) : Walter Roberson le 21 Fév 2022
ntables=10;
nlines=10;
ncolumns1=10;
ncolumns2=15;
ncolumns3=20;
ncolumns4=25;
ncolumns5=30;
%now for some example data, just to illustrate that it works.
%in your real code, you would create your real M1, M2, M3, M4, M5
M1=randi(10,ntables, nlines, ncolumns1);
M2=randi(10,ntables, nlines, ncolumns2);
M3=randi(10,ntables, nlines, ncolumns3);
M4=randi(10,ntables, nlines, ncolumns4);
M5=randi(10,ntables, nlines, ncolumns5);
%The matrixes M1....M5 are filled with values, not only 0.
dataC = cat(3,M1,M2,M3,M4,M5);
whos dataC
Name Size Bytes Class Attributes dataC 10x10x100 80000 double
DGM le 21 Fév 2022
Then the first example should suffice to concatenate them.

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