How to extract random subset of images from a cell array?

Hi all,

I'm working on a code that imports all images in a given file and stores them in a cell array. I wish to extract a random subset (n=100) of those images and save them in a separate cell array. Functions like 'randperm' aren't compatible with cell arrays, and I've not been able to find a similar function that is.

Any suggestions?

Alternatively, a similar solution that imports a random 100 images from the folder and saves a step, is also welcome. Here is the base code (though it may not be necessary):

cd '/Users/Documents/MATLAB/Grain Shape/60-62.fld' % modify this to change directory (cd) to appropriate folder

images = dir('*.png'); % loading all .png files in the directory

% read, convert to greyscale, and save raw images

for i = 1:440 % adjust maximum number for number of images imported

im_{i} = imread(images(i).name);

im_{i} = rgb2gray(im_{i});

end

Answer 1

[Jan]

Of course randperm works with cell arrays:

random_subset = im_(randperm(numel(im_), 100));

This selects 100 elements in random order without repetitions.

A hint: Do not change the current directory. Each callback of a GUI or a timer could do this unexpectedly also. Use absolute path names instead:

folder = '/Users/Documents/MATLAB/Grain Shape/60-62.fld';
images = dir(fullfile(folder, '*.png'));
for i = 1:numel(images)
     im_{i} = imread(fullfile(folder, images(i).name));
     im_{i} = rgb2gray(im_{i});
end

And if you do not want to import all images, but only the random subset:

folder = '/Users/Documents/MATLAB/Grain Shape/60-62.fld';
images = dir(fullfile(folder, '*.png'));
images = images(randperm(numel(images), 100));
... as above

[Allison Lepp]

I must have misunderstood some previous question threads regarding that function! This does this trick, thanks for the prompt help Jan.