Eliminated zero value in the matrix.

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Francesco
Francesco 2014-2-21
评论： Francesco 2014-2-22
I have this variable formatted as following:
>> dist
dist =
0 7.5000 15.0000 16.7705 21.2132 16.7705 15.0000 7.5000
7.5000 0 7.5000 10.6066 16.7705 15.0000 16.7705 10.6066
15.0000 7.5000 0 7.5000 15.0000 16.7705 21.2132 16.7705
16.7705 10.6066 7.5000 0 7.5000 10.6066 16.7705 15.0000
21.2132 16.7705 15.0000 7.5000 0 7.5000 15.0000 16.7705
16.7705 15.0000 16.7705 10.6066 7.5000 0 7.5000 10.6066
15.0000 16.7705 21.2132 16.7705 15.0000 7.5000 0 7.5000
7.5000 10.6066 16.7705 15.0000 16.7705 10.6066 7.5000 0
I want to obtain a 8x7 array because I want to eliminate all the 0 element rows by rows. The structure of the files is always the same with the 0 value on the main diagonal. How can I do this?

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采纳的回答

Matt Tearle
Matt Tearle 2014-2-21
Personally, I'd question whether this is a great idea. A distance matrix is supposed to be square and symmetric, with dist(j,k) representing the distance between points j and k. Removing those diagonal elements destroys that structure, and I don't see what it gains you. But if there's a good reason to go ahead, you could do:
n = size(dist,1);
dist(1:(n+1):end) = [];
dist = reshape(dist,n-1,n);
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Matt Tearle
Matt Tearle 2014-2-21
@Walter: true, I shifted down instead of across. Add a transpose, I guess :) The 0 on the diagonal is a good point. But in that case, my personal preference would be to fill the diagonal with NaNs:
n = size(dist,1);
dist(1:(n+1):end) = NaN
min(dist)
(But I guess there are other cases where that would be annoying, too...)
@Francesco: I've added a comment on that other question about how my code works. But, no, I don't use the distances for that.
That said, if you find pairwise distances to be useful, and you have Statistics Toolbox, there's a function to do it for you: pdist. If you want the matrix form, use squareform as well:
coords = rand(8,2); % column 1 is x, column 2 is y
dist = squareform(pdist(coords));
Francesco
Francesco 2014-2-22
Matt the problem is that I want to obtain a 8x7 matrix. I have to eliminate the zero element rows by rows.

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更多回答（1 个）

Chad Greene
Chad Greene 2014-2-21
dist2 = repmat(dist(~eye(size(dist))),1,7)

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