Indexing question for member variables of opticalFlow collected into an MxN cell array

Question

Erick Oberstar 2020-6-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/546203-indexing-question-for-member-variables-of-opticalflow-collected-into-an-mxn-cell-array

编辑： Ameer Hamza 2020-6-11

I am attempting to find the maximum value over alll member variables (PxQ) for a multidimensional set of MxN opticalFlow system objects

Flow_PlaneA{TestNum,frame} loads up a single opticalFlow system object from a mat file

I would like to find max value of all something like:

VxMax = max(Flow_PlaneA{:,:}.Vx

VyMax = max(Flow_PlaneA{:,:}.Vy

Magnitude Max = max(Flow_PlaneA{:,:}.Magnitude

OrientationMax = max(Flow_PlaneA{:,:}.Orientation

This gives me an error for the VxMax equation for example:

"Expected one output from a curly brace or dot indexing expression, but there were " N "results." (where N = 802 for this data)

The only way I can seem to index is to do 2 nested loops for each member variable for example

for TestNum = 1:M

for frame = 1:N

VxMaxNew = max(max(Flow_PlaneA{TestNum,frame}.Vx )); % max(max( covers PxQ)

VxMax = max([VxMaxNew VxMax])

end

Is there an array type indexing based method to do this I am just missing? How do I handle the mix of opticalFlow objects (which look like structs to me) and the multidimensional cellarray indexing at the same time? Is that possible?

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

Ameer Hamza 2020-6-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/546203-indexing-question-for-member-variables-of-opticalflow-collected-into-an-mxn-cell-array#answer_449648

在 MATLAB Online 中打开

Try this

VxMax = [flow{:}];
VxMax = max([VxMax.Vx]);

or alternatively

VxMax = max(cellfun(@(x) x.Vx, flow), [], 'all');

5 个评论
显示 3更早的评论隐藏 3更早的评论

Erick Oberstar 2020-6-11

A little big but here it is: https://uwmadison.box.com/s/8be2s8die5y3y5imzyf8xd49vvcxnxq1

Ameer Hamza 2020-6-11

编辑：Ameer Hamza 2020-6-11

在 MATLAB Online 中打开

The solution could have been more efficient, but some of the cells are empty. The solution requires the creation of an intermediate variable. Try the following two alternatives

maxVx = max(arrayfun(@(x) max(max(x.Vx)), [Flow_PlaneA{:}]));

or

maxVx = max(max(cellfun(@helperFun, Flow_PlaneA)));
function y = helperFun(x)
    if ~isempty(x)
        y = max(max(x.Vx));
    else
        y = -inf; % smallest value
    end
end