how can i avoid the for loop in this case?

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Dror Aizik 2020-5-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/524828-how-can-i-avoid-the-for-loop-in-this-case

评论： Dror Aizik 2020-5-12

a_matrix=zeros(10,4);
a=[3 6 7 8]';
for i=1:numel(a)
    a_matrix(a(i),i)=1;
end
disp(a_matrix)
     0     0     0     0
     0     0     0     0
     1     0     0     0
     0     0     0     0
     0     0     0     0
     0     1     0     0
     0     0     1     0
     0     0     0     1
     0     0     0     0
     0     0     0     0

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Answer 1

Stephen23 2020-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/524828-how-can-i-avoid-the-for-loop-in-this-case#answer_431955

编辑：Stephen23 2020-5-12

在 MATLAB Online 中打开

Method one: logical equals:

>> a = [3,6,7,8];
>> V = 1:10;
>> M = double(V(:)==a) % requires MATLAB >= R2016b
M =
 0   0   0
 0   0   0
 0   0   0
 0   0   0
 0   0   0
 1   0   0
 0   1   0
 0   0   1
 0   0   0
 0   0   0

For earlier MATLAB versions replace == with bsxfun.

Method two: sub2ind:

>> M = zeros(10,4);
>> X = sub2ind(size(M),a,1:4);
>> M(X) = 1
M =
 0   0   0
 0   0   0
 0   0   0
 0   0   0
 0   0   0
 1   0   0
 0   1   0
 0   0   1
 0   0   0
 0   0   0