Duplicating rows in a matrix

Question

Edward Johnsen 2019-1-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/441166-duplicating-rows-in-a-matrix

编辑： Stephen23 2022-1-5

采纳的回答： Star Strider

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Hi there

I have a matrix that i need to make twice as long. i.e i need to double the length of columns. eg i need:

[0 1 0 0]
[0 2 0 0]

to become:

[0 1 0 0]
[0 1 0 0]
[0 2 0 0]
[0 2 0 0]

Thanks

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Stephen23 2022-1-3

编辑：Stephen23 2022-1-5

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Just use REPELEM: https://www.mathworks.com/help/matlab/ref/repelem.html

A = [0,1,0,0;0,2,0,0]
A = 2×4
     0     1     0     0
     0     2     0     0
B = repelem(A,2,1)
B = 4×4
     0     1     0     0
     0     1     0     0
     0     2     0     0
     0     2     0     0

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Answer 1

Star Strider 2019-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/441166-duplicating-rows-in-a-matrix#answer_357752

编辑：Star Strider 2019-1-23

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Try this:

M = [0 1 0 0
     0 2 0 0];
M2 = repmat(M, 1, 2);
M2 = reshape(M2', [], 4)'

producing:

M2 =
   1     0     0
   1     0     0
   2     0     0
   2     0     0

You could combine both calculations into a one-line calcualtion if you want to.

EDIT —

Generally, for ‘N’ repitions, the code becomes:

N = 4;                                  % Number Of Repititions
Mn = repmat(M, 1, N)
Mn = reshape(Mn', [], 2*N)'
producing: 
Mn =
     0     1     0     0
     0     1     0     0
     0     1     0     0
     0     1     0     0
     0     2     0     0
     0     2     0     0
     0     2     0     0
     0     2     0     0

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Stephen23 2022-1-3

编辑：Stephen23 2022-1-3

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@Matthew Allison if you think that is elegant, just wait until you see REPELEM in action:

M = [0,1,0,0;0,2,0,0]
M = 2×4
     0     1     0     0
     0     2     0     0
Mn = repelem(M,2,1)
Mn = 4×4
     0     1     0     0
     0     1     0     0
     0     2     0     0
     0     2     0     0