MATLAB: Label segments based on percentage

celllabel;labellinglengthMATLABmatrixpercentagesegmentvariable

Hi,

I have a variable (AL_128 which I have attached). It is a 1×48 cell where each cell is a Ax20 matrix. The matrices contain the values 0 and 1. For instance, cell 1 is a 225×20 matrix which should be interpret as follows: 225 segments where each segment is of length 20.

What I want to do here is to say that if 30% of the segments contain the label 1, the whole segment should be labelled 1. Therefore, cell 1 will end up being a 225×1 vector. This should be done for all segments and all cells.

How can I do that?

Best Answer

Much simpler code:

threshold = 0.3;  %30% threshold
M = cellfun(@(m) mean(m, 1) >= threshold, AL_128, 'UniformOutput', false)

Or if you really want to use a loop over the cell array:

M = cell(size(AL_128));
for cidx = 1:numel(AL_128)
    M{cidx} = mean(AL_128{cidx}, 1) >= threshold;
end

There is certainly no need to loop over the columns of the matrix.

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MATLAB: Prolem in sparse

Huda, try this (edited to update with comments):

% Make Data
x=sparse(10,10);
x(1:10,1:10)=5;
% Get the rows, cols, values of any non-zero elements
[rows,cols,vals] = find(x);
% Save to a text file
fid = fopen('myFile.txt','w')
fprintf(fid, '(%d,%d)\t%f\n',[rows,cols,vals]')
fclose(fid)

And then to later open and read it:

fid = fopen('myFile.txt','r');
[R,C,V] = textscan(fid, '(%d,%d)\t%f');
fclose(fid)

Keep in mind a few things:

1. If you only want to save these files then read them back into MATLAB, it's much simpler to use save() and load(). For example:

myData = {[2 5 32], [1 2 3 4 5 6 7], [12 23 34]};
save('myFile.mat', 'myData')
clear myData       % This just deletes the variable "myData"
load('myFile.mat') % This just loads it again!

2. If you're setting the value of every element in a sparse matrix to a non-zero value, then you shouldn't be using a sparse matrix in the first place... sparse matrices are the most efficient when the majority of elements in your matrix are zeros. Instead, you should use a cell array of vectors like this:

myData = {[2 5 32], [1 2 3 4 5 6 7], [12 23 34]};
for i = 1:length(myData)
  for j = 1:length(myData{i})
     fprintf('Cell #%d, Element #%d, equals %f\n', i, j, myData{i}(j))
  end
end

MATLAB: Manipulate data in cells

Hi Rebecca,

I think it would be easiest just to loop through all of the elements of the matrix. To access a given element in the cell array 'bins', use the curly braces {}, in a way that you similarly would use parentheses () for matrices.

For the first part:

 output = cell(size(bins));
 for k=1:length(bins), 
     mat = bins{k};   %get element in cell

     mat(:,5)=[];     %remove 5th column

     output{k} = mat;  %assign to output cell array 
end

The second part of your request is unclear. Once you break each row into four separate groups of three columns, what do you want to do with the data? Are you assigning each group as an element of the cell array (such that the final cell array is 255x4)? If so, this revised code will work:

 output = cell(length(bins), 4);
 for k=1:length(bins), 
     mat = bins{k};   %get element in cell
     mat(:,5)=[];     %remove 5th column
     output{k,1} = mat(:,[1 2 3]);  %break columns into groups and 
     output{k,2} = mat(:,[1 2 4]);  % assign to cell array
     output{k,3) = mat(:,[1 3 4]);
     output{k,4} = mat(:,[2 3 4]);
end

Best Answer

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MATLAB: Prolem in sparse

MATLAB: Manipulate data in cells

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