Repmat a vector n times where n is not a whole number

Question

Stef 2018-6-24

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编辑： Ankita Bansal 2018-6-25

I have a vector y consisting out of 10 elements. I want have a for loop, where I repmat the vector y to a new vector. However repmat is not working since n is not always a whole number. In this case I want it to choose the element which is next, e.g. if n = 4.2 it should take y 4 times and add element 1 and 2 separately. How can I do this?

y = [1:10];
for n = 4:0.5:6
Z = repmat(y,n,1);
end

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Stephen23 2018-6-25

编辑：Stephen23 2018-6-25

The square brackets are totally superfluous:

https://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets

Adam 2018-6-25

Also there were a couple of answers to essentially the same question here:

https://uk.mathworks.com/matlabcentral/answers/313282-repeating-a-vector-up-to-a-given-length

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Answer 1

Stephen23 2018-6-25

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编辑：Stephen23 2018-6-25

在 MATLAB Online 中打开

To take the smaller index (equivalent to fix):

>> y = 1:10;
>> n = 4.2;
>> [repmat(y,1,fix(n)),y(1:numel(y)*mod(n,1))]
ans =    1    2    3    4    5    6    7    8    9   10    1    2    3    4    5    6    7    8    9   10    1    2    3    4    5    6    7    8    9   10    1    2    3    4    5    6    7    8    9   10    1    2

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Stephen23 2018-6-25

编辑：Stephen23 2018-6-25

在 MATLAB Online 中打开

"could you please show me how to make the 12 times 3 matrix instead of a 4 times 9? I mean for a matrix of four rows that row 5 is the same as row 1"

I don't understand. My example shows a 4x3 matrix and n=2.5, which would give a 10x3 matrix. How do you expect to get a 12x3 matrix from that?

>> [repmat(y,fix(n),1);y(1:size(y,1)*mod(n,1),:)]
ans =
 9   4
 2   3
 4   9
 4   7
 9   4
 2   3
 4   9
 4   7
 9   4
 2   3

Stef 2018-6-25

Thank you very much, Stephen!

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Answer 2

Ankita Bansal 2018-6-25

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编辑：Ankita Bansal 2018-6-25

在 MATLAB Online 中打开

Hi Stef, are you saying that you have a 4x9 matrix A and you want to reshape it to 12x3? If so then you can use reshape function available in MATLAB.

But if you are saying that you want to create a 12x3 matrix B, where B(5,:) is equal to B(1,:) and B(6,:) is equal to B(2,:) and so on, then which elements from A do you want to drop?

Or are you saying that you want to create a 12x9 matrix from A? if so then also you can write

M= [repmat(y,fix(n),1);y(1:size(y,1)*mod(n,1),:)]