MATLAB Answers


Storing multiple value in array without overriding.

Asked by ALOK RAJ on 11 May 2019
Latest activity Commented on by ALOK RAJ on 14 May 2019
Below is the code snippet, where I am selecting images one by one, converting a image in 30*30 patch and calculating the standard deviation of patch and then storing that value in excel sheet. But the problem is only the standard deviation of last image is being saved to excel sheet others value are getting over ridden. How to avoid that?
Directory = 'With MA\';
%Imgs = dir(fullfile(Directory,'*.jpg'));
Imgs = dir(Directory);
nfiles = length(Imgs); % Number of files found
for z=1:nfiles
thisname = Imgs(z).name;
thisfile = fullfile(Directory, thisname);
Img = imread(thisfile);
%Img = imread(fullfile(Directory,Imgs(z).name));
imSz = size(I);
patchSz = [30 30];
xIdxs = [1:patchSz(2):imSz(2) imSz(2)+1];
yIdxs = [1:patchSz(1):imSz(1) imSz(1)+1];
patches = cell(length(yIdxs)-1,length(xIdxs)-1);%for patches
stan = cell(length(yIdxs)-1,length(xIdxs)-1);%for standard deviation
for i = 1:length(yIdxs)-1
Isub = I(yIdxs(i):yIdxs(i+1)-1,:);
for j = 1:length(xIdxs)-1
patches{i,j} = Isub(:,xIdxs(j):xIdxs(j+1)-1);%saving patches
stan{i,j} = std2(patches{i,j});%saving standard deviation
xlswrite('output.xlsx', stan);


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1 Answer

Answer by Stephen Cobeldick on 11 May 2019
Edited by Stephen Cobeldick on 11 May 2019
 Accepted Answer

"How to avoid that?"
Simply by changing the Excel worksheet name on each iteration of the outer loop, e.g.:
for z=1:nfiles
F = sprintf('output_%d.xlsx',z);
Or you could use fileparts to create a name based on the original image filenames, e.g.:
[~,N] = fileparts(thisname);
F = sprintf('%s.xlsx',N);
Note that you should place the xlswrite inside the try section, otherwise your code will export the results from the last imported file, without any warning. Placing so much code inside try is not a good idea, as this hides any errors and bugs in that part of the code. Better code would simply use exist to test for the file (rather than try). I doubt that try does anything useful here anyway, as dir only lists existing files anyway, so most likely you should get rid of try entirely.
Read this:


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The warning occurs because in the format string you escape the characters \U and \L and \D and \W , none of which are valid escaped characters. You also escape \o , which is valid for formatting octal numbers, but you do not supply an input value to use this format specifier.
You could resolve this by escaping the backslash itself or by supplying the path as an input argument, but I recommend to simply use fullfile:
F = sprintf('output_%d.xlsx',z);
Like I am saving standard deviation in xlsx file, in the same way if i save gamma value in other xlsx file and then I want to plot a graph between standard deviation vs gamma. How can I do that?

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