how can i avoid the for loop in this case?

2020 5 12
1 个回答
回答已采纳
更新时间：2020 5 12
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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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Stephen23
Stephen23 2020-5-12
编辑：Stephen23 2020-5-12

0 个投票

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
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
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
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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