Extracting multiple points from matrix and plotting

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Faizan Tahir
Faizan Tahir 2016-2-19
评论： Star Strider 2016-2-19
Hi.
I have a 900 row by 3 column matrix, each corresponding to a centroid of 3 objects. The 3 objects are red, green and blue.
The first column corresponds to the X coordinate, the second corresponds to Y coordinate of the objects centroid, and the 3rd column corresponds to the centroid's colour (1 = red, 2 = green, 3 = blue).
How can I efficiently loop through the matrix and filter all the rows where colour = 1, and plot all the coordinates from top to bottom, and same for the other two? I know this should be easily possible using find, but my matlab isn't great so any help is much appreciated.

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回答（1 个）

Star Strider
Star Strider 2016-2-19
I would use the sortrows function. It should be able to do what you want.
  1 个评论
Star Strider
Star Strider 2016-2-19
The best way to do that is with a cell array, to avoid creating dynamic variables (a poor programming practise). Here, ‘Mtx{1}’ has all the rows where the third column is 1, and so for the others. The rows remain the same.
The code:
M = [randi(99, 15, 2) randi(3, 15, 1)]; % Create Data
for k1 = 1:3
Mtx{k1} = M(M(:,3) == k1,:); % Create Cell Array
end

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