How do I randomly select k points from N points in MATLAB?

Question

I use this code to create and plot N points:

N=input(\'No. of Nodes:\');
data = rand(N,2) % Randomly generated n no. of nodes
x = data(:,1);
y =         


        

Answer 1

From what I understood, for each of the N random point you want to flip a coin to decide whether to select it or not (where the coin has a p=0.25 probability of success!)

data = rand(N,2);             %# generate random points
index = (rand(N,1) <= p);     %# roll coins to pick with prob p
data(~index, :) = [];         %# keep only selected points

This ends up being equivalent to only generating p*N random points in the first place (at least you approach this number as N grows larger)...

data = rand(p*N, 2);          %# directly generate p*N number of points

you can test that last statement for various values of N:

fprintf('1st = %d \n', p*N)
fprintf('2nd = %d \n', sum(rand(N,1) <= p))