Refresh random sample within a FOR loop

A have a data se of 1000 normally distributed values representing annual discount rate (dr). I wrote a code that randomly picks 20 values from the data set and assigns it to a formula that calculates net present value (npv) using those 20 values. What I want it to do is to run the simulation n-times and save the value of npv in a vector npvsim after each simulation. Numper of simulations is defined by u=length(npvsim), in this case 5.

What I get in results at the moment is the same value stored five times. It seems to me that i=randsample(dr,20) takes a sample once and the same values are then used for 5 times. Is there any way I can make these 20 values to be refreshed for each iterations? I'm kind of stuck and the existing answers provite little help.

Thank you in advance.

npvsim = zeros(5,1);

for  u = length(npvsim) ;
    
    %selecting 20 random discount rates for each year
    i = randsample(dr,20);
    
    for n = reshape(1:20,20,1);
        npv = -2000+ sum(571.5./((1+i).^n));
        npvsim(:,u') = npv;
    end;
end;

Answer 1

[Walter Roberson]

for  u = 1:length(npvsim)

[Evgeny Nikolaev]

It works and makes perfect sence, thank you!