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How to randomly generate one non-zero element of each row from a matrix

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Chaoyang Jiang
Chaoyang Jiang 2018-7-3
编辑： Stephen23 2018-7-3
How to randomly generate one non-zero element of each row from a matrix and then create a new matrix?
For A=[1 5 6 7 0; 2 0 0 4 2; 0 0 3 4 0]; I want to have a random vector B where each element in B (non-zero) is randomly generated from A. e.g., B=[1,2,3] or [5 4 3] or [7 2 3]...

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回答（2 个）

Rik
Rik 2018-7-3
There's probably a faster way, but the code below should work.
A=[1 5 6 7 0; 2 0 0 4 2; 0 0 3 4 0];
A_cell=cellfun(@(x) x(x~=0),...
mat2cell(A,ones(1,size(A,1)),size(A,2)),...
'UniformOutput',false);
B=arrayfun(@(x) x{1}(randi(numel(x{1}))),A_cell);
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Stephen23
Stephen23 2018-7-3
"This line might in a loop that will be repeated 10,000 times. I am hoping there will be an efficient way."
@Chaoyang Jiang: why not just generate all random selection at once? Is a loop strictly required?

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Stephen23
Stephen23 2018-7-3
编辑：Stephen23 2018-7-3
In two lines:
>> A = [1,5,6,7,0;2,0,0,4,2;0,0,3,4,0];
>> [R,C] = find(A);
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
5
2
3
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
7
2
3
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
5
2
3
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
6
4
3
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
7
2
3
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
6
2
4
>> accumarray(R,A(A~=0),[],@(v)v(randi(numel(v))))
ans =
5
2
3
Or slightly more clearly:
[R,~] = find(A);
fun = @(v)v(randi(numel(v)));
B = accumarray(R,A(A~=0),[],fun)

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