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making column of zero matrix equal to one based on another matrix

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Sukuchha
Sukuchha 2014-2-25
评论： Image Analyst 2014-2-26
Hi ,
I have a zero matrix (A) of size mxn where m in number of observation and n number of feature. I have another non zero matrix (B) of size (mx1) where numbers respresent column in matrix A which should be replaced by one.
How to do this ?

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采纳的回答

Jos (10584)
Jos (10584) 2014-2-25
Perhaps you want to set in a row K of A, the entry in column B(k) to one?
%data
A = zeros(3,3)
B = [3; 1; 2] % column index
% engine
R = 1:numel(B) % row index
idx = sub2ind(size(A), R, B) % convert to linear indices into A
A(idx) = 1
Note that the statement A(R,B) = 1 does not do what you might think it should do.
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Jos (10584)
Jos (10584) 2014-2-26
@Image Analyst My apologies, I should have tested the code properly, rather than write it down theoretically.
@Sukuchha, I am glad you solved this issue yourself.
Image Analyst
Image Analyst 2014-2-26
No problem - I sometimes post untested code off the top of my head also, and mistakes do happen. Actually I'm kind of impressed that you (1) actually figured out what he meant, and (2) thought up that somewhat cryptic solution off the top of your head.

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更多回答（1 个）

Image Analyst
Image Analyst 2014-2-25
Did you try
A(:, B) = 1;
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Paul
Paul 2014-2-25
编辑：Paul 2014-2-25
Well, that is what you said you want. Since all three the column indices are present in B, all values of A are set to 1.
Image Analyst
Image Analyst 2014-2-25
编辑：Image Analyst 2014-2-25
I agree with Paul. You said any column number of A that shows up in B should have that entire column of A set to 1. For example:
A = randi(9, 5, 8) % Random integers
B = [1,3,7]; % Set columns 1, 3, and 7 to all 1's.
A(:, B) = 1

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