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)

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.

Answer 1

[Jonas]

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

[Myssipsa Mehraz]

Sorry, but this don't really do what i want. Maybe it's me who don't know how to use it. Can you please give more details?

Thank you in advance.

[Jonas]

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]

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

Thank you.

Answer 2

[Stephen23]

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

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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

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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

[Jonas]

thumbs up for that solution!