replace zeros according to distribution of integers in each column

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J T 2016-10-22

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评论： J T 2016-10-23

if I have some matrix x of randomly distributed values (value 0 to n = 5 or 10 in this case)

x = [binornd( 5, 0.05, 10000, 1 ), binornd( 10, 0.1, 10000, 1 )];

I want to create a second matrix where any zeros in x are replaced at random by a value from 1 to n according to the distribution when zero is excluded in that particular column. I want to do this by random sampling from the values in each column excluding zero.

Any ideas how to do this quickly (in reality the matrices are considerably bigger than this example...)

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Answer 1

Guillaume 2016-10-22

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编辑：Guillaume 2016-10-22

在 MATLAB Online 中打开

If I understand correctly, you want to replace all zeros in a column by random non-zero values from the same column? In which case:

replacementcount = sum(x == 0);
for column = 1:size(x, 2)
   validvalues = nonzeros(x(:, column));
   x(x(:, column) == 0, column) = validvalues(randperm(numel(validvalues), replacementcount(column)));
end

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Guillaume 2016-10-22

The error with randperm is because you have more 0s in the column than non-zeros, something I had not considered.

Because the number of 0s can vary per column you cannot avoid the loop. Note that it's only looping over the columns whose number I understood is negligible compared to the number of rows.

J T 2016-10-23