# How to insert rows into a matrix

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Elaheh am 14 Dez. 2018
Kommentiert: Mohsin Shah am 15 Apr. 2019
Hi
I have a matrix (748*6). I need to insert one row after every 3rd row. How should I do that? the resulting martix should be (1126 *6).
Thank you
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Jan am 14 Dez. 2018
Bearbeitet: Jan am 14 Dez. 2018
This cannot work. "After every 3rd row" means, that the number of rows would grow by 4/3. Example with 6 elements:
[1,2,3,<insert>, 4,5,6,<insert>]
Maybe you mean "after every 2nd row" or "in every 3rd row". Then the number of rows grows by a factor of 3/2. This is near to the given sizes, but not exactly: 748 / 2 * 2 is 1122, not 1126.
Please post a short example with inputs and outputs to clarify, what you want.
You did not mention what you want to insert: zeros, NaNs, values from another matrix? "Inserting rows" is not clear in this point.
Elaheh am 14 Dez. 2018
apologize for not being clear. This is one part of data. Current table is on the right and the one I need to create is on the left.

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### Akzeptierte Antwort

Jan am 14 Dez. 2018
If the details with the size of the output are cleared, something like this will solve the problem:
A = rand(748, 6); % Test data
n = 3; % In each 3rd row
m = true(748 / (n-1) * n, 1);
m(n:n:end) = false;
B = zeros(numel(m), 6);
B(m, :) = A;
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Mohsin Shah am 15 Apr. 2019
Awsome!

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