How to set value in a matrix
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I have a double matrix 4x5 matrix
A=[11 12 13 14 15;
21 22 23 24 25;
31 32 33 34 35;
41 42 43 44 45],
B=[3 0 2 4 1]
B indicates to set all the rows of B[i] in A(from row 1 to that position) to 0.
C = [0 12 0 0 0;
0 22 0 0 25;
0 32 33 0 35;
41 42 43 0 45]
Thanks
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Adam Danz
2020년 2월 5일
for i = 1:numel(B)
A(1:B(i),i) = 0;
end
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Adam Danz
2020년 2월 5일
편집: Adam Danz
2020년 2월 5일
Thanks for the timing comparisons, Rik!
One way around the limitations to timeit is by increasing the size of the arrays. With the large array inputs below, both of your solutions are faster.
A = randi(10000,1000);
B=randi(10000,1,1000)-1;
ans =
0.18254 % fun1 (my loop)
ans =
0.026578 % fun2
ans =
0.026723 % funct_compact
추가 답변 (1개)
Rik
2020년 2월 5일
This was a fun puzzle. I believe the code below is one of the many possible solutions. It does use implicit expansion, so for pre-R2016b you will have to use bsxfun.
A=[11 12 13 14 15;
21 22 23 24 25;
31 32 33 34 35;
41 42 43 44 45];
B=[3 0 2 4 1];
a=-(1:size(A,1))';
L= a+B(:)' >=0; %the (:)' is to ensure B is a row vector
C=A;C(L)=0
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Rik
2020년 2월 6일
Thank you. While I like the one-linerness of the compact version, I think it looks like voodoo witchcraft, so I decided to post this as the answer
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