"nchoosek" function for a matrix whose all elements are 0 or 1

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Ismaeel 2016-12-29

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https://ww2.mathworks.cn/matlabcentral/answers/318456-nchoosek-function-for-a-matrix-whose-all-elements-are-0-or-1

评论： Ismaeel 2016-12-29

采纳的回答： James Tursa

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I have a matrix A whose all elements are 0 or 1. For example, the first row of A is:

[ 0 0 1 0 0 1 0 1 0 0]

I want to use nchoosek function to find the combinations of (total number of 1's in a row) -1. Here, n= 3, k=n-1=2 (always k=n-1). How can I apply this function to all the rows of the matrix or at least, for the above vector.

The output should be as:

[   0     0     1     0     0     1     0     0     0     0]
[   0     0     1     0     0     0     0     1     0     0]
[   0     0     0     0     0     1     0     1     0     0]

nchoosek (3,2)=3.

Thanks

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the cyclist 2016-12-29

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For the example

A = [0 0 1 0 0 1 0 1 0 0]

you want all possible rows that have two 1's and how many 0's?

Ismaeel 2016-12-29

Thanks, yes all possible 1's without considering the 0's. But I want the locations of these possible 1's to be kept.

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Answer 1

James Tursa 2016-12-29

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https://ww2.mathworks.cn/matlabcentral/answers/318456-nchoosek-function-for-a-matrix-whose-all-elements-are-0-or-1#answer_248829

编辑：James Tursa 2016-12-29

在 MATLAB Online 中打开

E.g., using a loop:

f = find(A);
n = numel(f);
result = repmat(A,n,1);
for k=1:n
    result(k,f(k)) = 0;
end

Or if the order matters:

result(k,f(n-k+1)) = 0;

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Ismaeel 2016-12-29

So Cool, thank you so much James.

Ismaeel 2016-12-29

Can we modify the code in case if A is a matrix instead of a vector? let's say: A=[0 0 1 0 0 1 0 1 0 0] [0 1 0 0 0 1 0 0 0 0] Thanks once again

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