Presenting faces at random without repetition

I need help in presenting a set of images (10 in total, at random without any repetitions. In the files, however, I have a total of 20 images and only certain specific pictures have been decided to be presented. How do I specify such criteria? Also, I tried to insert a specification where each of the pictures will be presented for 2 seconds but could not seem to figure out where shall the code be put at.

The following are the codes that I have written but it does not seem to comply. If there are any correction please do help me.

%loop start for recognition phase

%where my codes actualy START

A = imread('matlabfaces');

B = ['x','y','z'];

C = B(randi(numel(B)));

files = dir('matlabfaces'); %specify again the file location

numberoffiles = length(files); %total amount of files?

randomIndexs = randperm(numberoffiles); %randomise the files

%start loop

for j = 1:numberoffiles

thisFilename = files(randomIndexs(j)).name;

rgbimage = imread('matlabfaces');

image (rgbimage);

axis('image', 'off');

pause(3);

end

sca;

[John D'Errico]

Please don't keep on posting the same question. If you don't understand the answer, then say so, and ask for further explanation.

Answer 1

[John D'Errico]

Pick the 10 images to be shown immediately, as 10 numbers from the set 1:23, WITHOUT replaceemt. randperm will do that for you. Then just display the chosen images in that sequence.

help randperm

 RANDPERM Random permutation.
    P = RANDPERM(N) returns a vector containing a random permutation of the
    integers 1:N.  For example, RANDPERM(6) might be [2 4 5 6 1 3].
 
    P = RANDPERM(N,K) returns a row vector containing K unique integers
    selected randomly from 1:N.  For example, RANDPERM(6,3) might be [4 2 5].
    
    RANDPERM(N,K) returns a vector of K unique values.  This is sometimes
    referred to as a K-permutation of 1:N or as sampling without replacement.
    To allow repeated values in the selection, sometimes referred to as
    sampling with replacement, use RANDI(N,1,K).
 
    RANDPERM calls RAND and therefore changes the state of the random number
    generator that underlies RAND, RANDI, and RANDN.  Control that shared
    generator using RNG.
 
    See also NCHOOSEK, PERMS, RAND, RANDI, RNG.

    Documentation for randperm
       doc randperm

    Other uses of randperm

       gpuArray/randperm    RandStream/randperm

So all you need is

randomIndexs = randperm(numberoffiles,10); %randomise the files

ans = 1×10

1 7 3 20 8 22 9 4 14 18

And now your for loop will start out as:

for j = 1:10

As far as the 2 second pause goes, you already have it doing a 3 second pause. That is what pause(3) should do. Perhaps you are not counting the seconds carefully when you look at it? Or perhaps, even though you say you want a 2 second pause, you really want a longer pause and do not realize it?