Assigning Null / Multi-Dimensional Matrix

Question

tinkyminky93 2022-4-7

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回答： Arif Hoq 2022-4-7

Hello,

I have a matrix with the dimensions of 4x2500 and I am generating this matrix in for loop. I want this matrix to be 4x1250. Without multi dimension I just write A(1:length(X)) = [] but I am stuck in multi dimension. This logic does not work in my operation.

when I say

A = [1:1:2500];

A (1:1250) = [];

it works and that is what i want to do.

but in multi dimension,

for i = 1:1:4

A(i,:) = ????????

end

Can someone help me? Thanks.

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KSSV 2022-4-7

Question is not clear. What you want to do in the loop?

tinkyminky93 2022-4-7

I have an array and I am writing this array to every row of the matrix. For example lets say I have [1:1:5]. What I do in for loop is

A(i,:) = my array

i'th row : 1 2 3 4 5

i+1'th row: 1 2 3 4 5

i+2'th row: 1 2 3 4 5

i+3'th row: 1 2 3 4 5

I want to assign null to every row of this matrix, then it will become

i'th row : 4 5

i+1'th row: 4 5

i+2'th row: 4 5

i+3'th row: 4 5

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Answer 1

Arif Hoq 2022-4-7

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在 MATLAB Online 中打开

vectorized solution is the most efficient and simple. But, still if you need for loop, try this

x=1:5;
A = repmat(x,4,1); 
for i = 3:-1:1  % if you want to delete from Column 3 then index i will be started from 3. 
    A(:,i) = []
end

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Answer 2

KSSV 2022-4-7

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A = repmat(1:5,4,1)
A = 4×5
     1     2     3     4     5
     1     2     3     4     5
     1     2     3     4     5
     1     2     3     4     5
A(:,1:3) = []
A = 4×2
     4     5
     4     5
     4     5
     4     5

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tinkyminky93 2022-4-7

编辑：tinkyminky93 2022-4-7

Can you try it with for loop? Will it be the same? I am getting error when i try

A = repmat(1:5,4,1);

for i = 1:1:4

A(:,1:3) = [];

end

>> Matrix index is out of range for deletion

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