how to put the same value in a number of lines in the first column of a matrix and different values in the second column (values coming from vectors)

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Myssipsa Mehraz 2021-6-26

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编辑： Stephen23 2025-7-27

Hello everyone,

My problem is that i have to report values from 2 vectors (of positions) in a matrix of (nx2), and for each value of the first vector (first columns) i should have m values in the second column and so on.

EXAMPLE :

vect_1=1:1:2;

vect_2=1:1:4;

%i want have this in my matrix

1 1

1 2

1 3

1 4

2 1

2 2

2 3

2 4

I'm a debutant in Matlab, so i tried some loops but it never does what i want.

Thank you, for helping.

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Answer 1

Jonas 2021-6-26

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for the first column have a look into repelem(), for the second column have a look into repmat()

if you need more detailed help, just tell us

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Jonas 2021-6-27

在 MATLAB Online 中打开

does this exanple help you? nrOfReps is the number of tepetitions of vector 2 and repelem repeats the elemts of vector 1 according to vector length of vector 2 compared to length of vector 1 and number of tepetitions of vector 2

nrOfReps=2;
vect1=(1:2)';
vect2=(1:4)';
mat(:,1)=repelem(vect1,length(vect2)/length(vect1)*nrOfReps);
mat(:,2)=repmat(vect2,[nrOfReps 1])

Myssipsa Mehraz 2021-6-29

It does exactly what i want. Now i have to expand it for several vectors.

Thank you.

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Answer 2

Stephen23 2021-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/865825-how-to-put-the-same-value-in-a-number-of-lines-in-the-first-column-of-a-matrix-and-different-values#answer_735888

编辑：Stephen23 2025-7-27

在 MATLAB Online 中打开

The simple MATLAB approach is to leverage NDGRID:

v1 = 1:1:2;
v2 = 1:1:4;
[m2,m1] = ndgrid(v2,v1);
m = [m1(:),m2(:)]
m = 8×2
     1     1
     1     2
     1     3
     1     4
     2     1
     2     2
     2     3
     2     4
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

Can be extended to any number of vectors (although you will run out of memory very quickly):

C = {v1,v2}; % any number of vectors
N = numel(C);
[C{end:-1:1}] = ndgrid(C{end:-1:1});
m = reshape(cat(N+1,C{:}),[],N)
m = 8×2
     1     1
     1     2
     1     3
     1     4
     2     1
     2     2
     2     3
     2     4
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

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Jonas 2021-6-30

thumbs up for that solution!

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how to put the same value in a number of lines in the first column of a matrix and different values in the second column (values coming from vectors)

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how to put the same value in a number of lines in the first column of a matrix and different values in the second column (values coming from vectors)

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