MATLAB: 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???…

Best Answer

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

Related Solutions

MATLAB: Split array into training and testing based on label

Try this:

A      = rand(500,4);
labels = randi([1,4],500,1);
A(:,4) = labels;
% Filter data based on labels
A_1 = A(A(:,4)==1,:);
A_2 = A(A(:,4)==2,:);
A_3 = A(A(:,4)==3,:);
A_4 = A(A(:,4)==4,:);
 
% Training and test data for first label
% Generate training indices
train_ind           = sort(randperm(size(A_1,1),ceil(0.7*size(A_1,1))));
% Get the remaining indices for testing dataset
test_ind            = 1:size(A_1,1);
test_ind(train_ind) = [];
A_train_1           = A_1(train_ind,:);
A_test_1            = A_1(test_ind,:);
% Repeat the same for other labels

Change 0.7 in the train_ind line to whatever percent data you would like for training set.

Hope this helps.

MATLAB: How to replace half the number of specific element in an array

To change random columns:

>> A=[1 2 3 4 4 1 2 4 4 3 4 4 4 2 1 3 4 4 4 2 1 4 4]
A =
   1   2   3   4   4   1   2   4   4   3   4   4   4   2   1   3   4   4   4   2   1   4   4
>> nnz(A==4)
ans =  12
>> idx = find(A==4);
>> num = numel(idx);
>> A(idx(randperm(num,ceil(num/2)))) = 2
A =
   1   2   3   2   2   1   2   4   4   3   2   4   2   2   1   3   2   4   4   2   1   2   4
>> nnz(A==4)
ans =  6

Best Answer

Related Solutions

MATLAB: Split array into training and testing based on label

MATLAB: How to replace half the number of specific element in an array

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