How can i do leave-one-out for classification?

Question

Sara Salimi 2017-5-23

0
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https://ww2.mathworks.cn/matlabcentral/answers/341552-how-can-i-do-leave-one-out-for-classification

回答： Matthew Taliaferro 2017-5-23

Hi

I have 110 stack of images (110 different patients), and I have extracted each patients features which is a matrix (2,400,000 x 135) and the ground truth (labels) for each (2400000 X 1). The task that I am doing is classifying each pixel. I have saved these images in two cells (here i have brought only three patients for simplicity):

featCell=1x3 cell (2,400,000 x 135 inside each cell)
lbcell=1x3 cell (2400000 X 1 inside each cell)

I want to do feature selection and then classification with knn classifier. Beside I want to apply leave-one-out cross validation (take one patient out as test and the rest two patients as train). I do not know how to do leave-one-out for these cells? If I save in matrix, it is not possible since I have millions of rows. My questions are as follows:

What data structure is proper for saving this high amount of data? Is is good to save in cell as I have already done?
how to do feature selection on these feature cells? because I do not have all of them is one matrix.
I did these part, but I do not know hoe to proceed for feature selection and later for classification using LOO.

    N=length(featCell);
      M=1;
      for i=1:length(featCell)
          [Train, Test] = crossvalind('LeaveMOut', N, M); 
          Train_ind = find(Train);  % finding the indices of those cells for training
          Test_ind=find(Test);   % finding the indices of those cells for validation
    %%%I do not what to do here???
      end