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

2012 11 30
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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???...

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Jan
Jan 2012-11-30
编辑：Jan 2012-11-30

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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

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sani ars
sani ars 2012-11-30
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)
Jos (10584) 2012-11-30
if tr(i,1) == 5, tr(i,1) = 1 ; end

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Matt Fig
Matt Fig 2012-11-30

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labels(randperm(numel(labels)))

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sani ars
sani ars 2012-11-30
I just want to change the values of selected indexes, not the whole labels

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