I have a 4x4 array of 1's and I need to turn 3 of 4 ones to zero per row at random. So there will be a one 1 left in each row.

A = [1 1 1 1; 1 1 1 1; 1 1 1 1; 1 1 1];
B = [1 0 0 0;  0 0 1 0; 0 1 0 0; 0 0 0 1]; % An example 

[Image Analyst]

OK, thanks (I guess) for the announcement. Good luck with it. Have fun. 🙂

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[Torsten]

Better start with a zero matrix and replace one of the four zeros by a one in each row.

Answer 1

[Jan]

Instead of starting with ones and set all but one to zero, it is cheaper to start with zeros and set one element to 1 per row:

n = 4;
A = zeros(n, n);
A(sub2ind([n, n], 1:n, randi([1,n], 1, n))) = 1

A = 4×4

0 1 0 0 0 0 0 1 0 0 1 0 0 0 0 1

[the cyclist]

Edited to turn a rogue 4 into an n.

[Jan]

@the cyclist: Thanks.

Answer 2

[the cyclist]

Here is one way:

N = 4;

x = (1:N)';
y = randi(N,N,1);

linearIndex = sub2ind([N,N],x,y);

B = zeros(N,N);
B(linearIndex) = 1

B = 4×4

0 1 0 0 0 0 0 1 0 0 1 0 0 0 1 0