randomly divide vector into 2 parts.

i have vector 100000*1 .i want to randomly divide data of it into 80% and 20% and store them into 2 vector.Divide of data must be random.

"non_zero_entry" is total how many entry in the vector.i tried to do this but it show me error "Index exceeds the number of array elements (80000)".

training_data=.8;
tf = false(length(non_zero_entry),1);
tf(1:round(training_data*non_zero_entry)) = true;
tf = tf(randperm(non_zero_entry));  % error occur in this line "Index exceeds the number of array elements (80000)". 
dataTraining = index_rating(tf,:); 
dataTesting = index_rating(~tf,:);

Thanks in advance for your help.

Answer 1

[Rik]

I don't fully understand every step of your code, so I rewrote it:

index_rating=rand(100000,5);%generate example data
training_data=.8;

s=rand(size(index_rating,1),1);
sorted=sort(s);
cutoff=sorted(round(training_data*numel(s)));
tf=s<=cutoff;
dataTraining = index_rating(tf,:); 
dataTesting = index_rating(~tf,:);

Answer 2

[Bruno Luong]

For the record, here is how I would do:

n = size(index_rating,1);
i = randperm(n,round(training_data*n));

dataTraining = index_rating(i,:); 
dataTesting  = index_rating(setdiff(1:n,i),:);

Answer 3

[Bruno Luong]

Always post complete code that can run. don't less us geuss what is the size/class of the inputs

First assumption: non_zero_entry is a integer scalar, then change the allocation to

tf = false(non_zero_entry,1);

Second assumption non_zero_entry is a vector then change

tf = tf(randperm(non_zero_entry));

to

tf = tf(randperm(end))

Similarly correction must be applied for the earlier instruction

tf(1:round(training_data*end)) = true