How To Generate Non Repeating Random Numbers from 1 to 49

Hi,

Does anybody know how to generate a series of 10 non-repeating random integers between 1 and 49?

So far I've tried using p = randperm(50); p = p(1:10)-1; but this can give me 0 in my series of 10 random integers :/

Thanks

Answer 1

[Wayne King]

 p = randperm(49);
 p = p(1:10);

Or just

 p = randperm(49,10);

[Royi Avital]

What if N is very very large?

[Steven Lord]

No problem if you're using a release that supports the two-input syntax [release R2011b or later, according to a quick search.] In release R2015a, this takes a small fraction of a second on my machine:

 p = randperm(1e10, 10);

I wouldn't recommend trying Wayne's first approach with N = 1e10 if you're using an older release that does NOT support the two-input syntax.

[Samiu Haque]

What if it doesn't start with 1

For example:

Not repeating 10 random numbers in between 20 to 50

[Steven Lord]

Generate 10 random numbers in the interval [1, 31] (31 being the number of elements in the vector 20:50) and either add 19 or use them as indices into 20:50.

The former approach avoids explicitly creating the vector 20:50 (not a big deal for this example, a big deal if you're trying to select 10 elements from a very large range of values whose length you know.)

% Select 10 numbers from 100 to 1e7 without explicitly creating 100:1e7
UL = 1e7;
LL = 100;
numElements = UL-LL+1;
r = randperm(numElements, 10);
r + LL

The latter can be used even when the vector you're trying to sample has "holes" like the following.

x = 1:50;
x(mod(x, 5) == 0) = []
ind = randperm(numel(x), 6)
x(ind)

Answer 2

[Niraj Dalal]

p = randperm(49,10);