How can I get coordinates from a grouping inside of a matrix.

Question

Jonathan Salazar 2017-7-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/350731-how-can-i-get-coordinates-from-a-grouping-inside-of-a-matrix

回答： Image Analyst 2017-7-29

I have a matrix with 5 columns: atom number, mol_tag, then the x y and z coordinates. The mol_tag seperate the atoms into globules by sharing a common value, I need a matrix that will give three coordinates from each grouping of mol_tag so that I can calculate the normal vector to each of the mol_tag groupings. thank you!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2017-7-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/350731-how-can-i-get-coordinates-from-a-grouping-inside-of-a-matrix#answer_275997

在 MATLAB Online 中打开

mol_tags = YourMatrix(:,2)
unique_mol_tags = unique( mol_tags );
num_tags = length(unique_mol_tags);
mol_normals = zeros(num_tags, 3);
for K = 1 : num_tags
  three_idx = find( mol_tags == unique_mol_tags(K), 3, 'first');
  coords = YourMatrix(three_idx, 3:5);
  this_normal = ..... something with the coords
  mol_normals(K, :) = this_normal;
end

It is possible to code the coordinate finding part without any explicit loop, but I do not think the result would be any clearer, as it involves some advanced accumarray hacks.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Image Analyst 2017-7-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/350731-how-can-i-get-coordinates-from-a-grouping-inside-of-a-matrix#answer_276020

If by the "three coordinates from each grouping of mol_tag" you mean the mean x, y, and z over all rows with that mol_tag value, you can use grpstats() if you have the Statistics and Machine Learning Toolbox