MATLAB: Randomly divide vector into 2 parts.

Question

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

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,:);