G0064 : Operand missing

There appears to be a missing comma in the 'for' statement (fixed now in the tutorial). Here is the correct code:

rint = ceil(1e6 * rndu(2000, 1));

//Create vector to hold sample
samp = zeros(2000, 1);

//Sampling with replacement
for j(1, 2000, 1);
    idx = rint[j];
    samp[j,.] = A[idx,.];
endfor;

Also note, that you will need to create a matrix A before this from which to take samples. Here is a fully working example:

nobs = 1e6;
nvars = 5;

//Sample matrix to draw from
A = rndn(nobs, nvars);

rint = ceil(nobs * rndu(2000, 1));

//Create vector to hold sample
samp = zeros(2000, nvars);

//Sampling with replacement
for j(1, 2000, 1);
    idx = rint[j];
    samp[j,.] = A[idx,.];
endfor;

It is also helpful to know that in GAUSS 16 and newer, there is a function to take random samples with or without replacement. Here are two simple examples of that:

nobs = 1e6;
nvars = 5;

//Sample matrix to draw from
A = rndn(nobs, nvars);

//Sample without replacement
samp = sampleData(A, 2000);

//Sample with replacement
samp_wr = sampleData(A, 2000, 1);