Assign null to rows of a matrix

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Benedict Teng 2019-9-20

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评论： Benedict Teng 2019-9-20

Hi guys,

I wanted to assign increment rows of null to a variable "C". The variable C has a size of 138x6x69. My code is shown below.

a = 1;

for i = 1:69

C(1:a,:,i)=[];

a = a+2;

end

But the error was " A null assignment can have only one non-colon index.A null assignment can have only one non-colon index."

Can anyone teach me another way of modifying the code? I really need help.

Much Thanks

Ben

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Raj 2019-9-20

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You cannot assign 'null' like this to a 3D matrix while wanting to maintain the dimensions of the matrix. You can assign zero or NaN depending on what you want to achieve here.

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Stephen23 2019-9-20

编辑：Stephen23 2019-9-20

"but it seems like the matrix size change every time after I assign null the rows"

Because what you are doing is removing rows:

https://www.mathworks.com/help/matlab/math/removing-rows-or-columns-from-a-matrix.html

MATLAB does not have a "null" concept, even though you keep using this term. You can't "assign null" as you write, because "null" does not exist.

Can you suggest any better way to do this?

Collect all of the required indices into a vector, use it to remove all rows at once after the loop.

Benedict Teng 2019-9-20

I've got it, thanks for the advices guys. Really appreciate it.

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