Data Storage and Export From Matlab - excel

Question

Here is background information to the problem I am encountering:
1) output is a cell array, each cell contains a matrix of size = 1024 x 1024, type = double
2) labelbout is a cell array which is the identical to output, except that each matrix has been binarized.
3) I am using the function regionprops to extract the mean intensity and centroid values for ROIs (there are multiple ROIs in each image) for each cell of output
4) props is a 5 x 1 struct with 2 fields (centroid and mean intensity)
The problem: I would like to take the mean intensity values for each ROI in every matrix and export to excel. Here is what I have so far:
for i = 1:size(output,2)
props = regionprops(labelboutput{1,i},output{1,i},'MeanIntensity','Centroid');
end
for i = 1:size(output,2)
meanValues = getfield(props(1:length(props),'MeanIntensity'));
end
writetable(struct2table(props), 'advanced_test.xlsx');
There seem to be a few issues:
1) my getfield command is not working and gets the error: "Index exceeds matrix dimensions"
2) when the information is being stored into props, it overwrites the values for each matrix. How do I make props a 5 x n (where n = number of cells in output)?
Please help!!

Answer 1

1) my getfield command is not working and gets the error: "Index exceeds matrix dimensions"
An easier way to get numeric values out of the same field in an array of structs, as an array is: [structArray.fieldName]. In your case this will be:
meanValues = [props.MeanIntensity];
2) when the information is being stored into props, it overwrites the values for each matrix. How do I make props a 5 x n (where n = number of cells in output)?
One option would be to preallocate an empty cell of the necessary dimensions and then fill it in with your regionprops output. Like this:
props = cell(size(output,1),1);
for k = 1:size(output,2)
props{k} = regionprops(labelboutput{1,k},output{1,k},'MeanIntensity','Centroid');
end
for k = 1:size(output,2)
meanValues = [props{k}.MeanIntensity];
end
...
Another option would be to combine your loops so that you can use your matrix data before it is overwritten. Like this:
for i = 1:size(output,2)
props = regionprops(labelboutput{1,i},output{1,i},'MeanIntensity','Centroid');
meanValues = [props.MeanIntensity];
% update this call to place props in non-overlapping parts of your file (e.g. append)
% writetable(struct2table(props), 'advanced_test.xlsx');
end
The bad thing about this second one is it has a file I/O step right inside your loop which can really slow things down; not to mention you will need to curtail your writetable call so it places the resulting table in non-overlapping regions of 'advanced_test.xlsx'.