how to change a number randomly???...

I have a column matrix that contains class labels in it. It has 35 rows... There are 4 class labels ( 1 2 3 4 )...

labels = [1 1 3 2 4 1 2 4 3 3 2 1 4 2 3 4 4 2 2 1 3 2 4 4 2 3 1 1 2 4 3 1 2 1 3] '

now I randomly select 5% of data from it as

N_of_labels= size(labels,1)

prcnt_labels = ceil(N_of_labels*5/100);

rng(1,'twister');

rand_class_index = randsample(N_of_labels,prcnt_labels);

labels(rand_class_index) = rem(labels(rand_class_index),4)+1;

the purpose of it to make the class labels noisy (changing the actual label).... Now here, rem() will always change the label 1 into 2 and 2 into 3 and so on... I need to change the labels randomly i.e. I want that 2 should be change to any number from 1 3 4 but not always to 3.... how can I do that???...

Answer 1

[Jan]

What about adding random values between 0 and 3 before REM:

rem(labels(rand_class_index) + randi([0, 3], prcnt_labels, 1), 4) + 1

If the label must be changed, use the range [1,3].

[EDITED after your comment]

randi([0,3]) replies number from 0 to 3. Then a value can be unchanged. If a change is obligatory, use the range [1,3] as mentioned already:

rem(labels(rand_class_index) + randi([1, 3], prcnt_labels, 1), 4) + 1

[sani ars]

I have tried it... just change it as:

 rem(labels(rand_class_index) + randi([1,4], prcnt_labels, 1),4)+1

its working fine..... But at some places it is not changing the label e.g. if the label is 4 it still remain 4 as the randi () is randomly giving the number..

For this, I tried to match the actual labels (of selected indices) with the changed one as:

 tr = zeros(size(rand_class_index,1),2);

 tr = rem(labels(rand_class_index) + randi([1,4], prcnt_labels, 1),4)+1

 labl_val = labels(rand_class_index)

 for i = 1:size(rand_class_index,1)

        if  tr(i,1)== labl_val(i,1)

             tr(i,1) = labl_val(i,1)+1; 

        end
  end
    labels(rand_class_index) = tr(:,1)

// I need to rewrite following line of code

    tr(i,1) = labl_val(i,1)+1;

because using this line, if the label (labl_val) is 4 it will become 5 and I don't want 5.. I want that it should be change to any number from 1 2 3..

Just need to correct this line... Can someone plz tell about it??..

[Jos (10584)]

if tr(i,1) == 5, tr(i,1) = 1 ; end

Answer 2

[Matt Fig]

labels(randperm(numel(labels)))

[sani ars]

I just want to change the values of selected indexes, not the whole labels