new in matlab, first question

hey, i'm trying to take a sample from a raw vector using myRandPerm. i had started in the folowing way:

function s=sample(x,n,seed)
if n>length(x)
  -1
else
  {don't know how exactly i can get myrandperm selecting n numbers from the x vector}
end
end

thank you...

[Dani Tormo]

Try to format the code for an ease reading. You have more info on the Help button up here.

[Jan]

What is your reason to implement myRandPerm instead of using the builtin randperm function?

The tags are used to classify the questions. Therefore "matlab" is not useful, because all questions concerns this topic. "randperm" would be much better.

Answer 1

[Sean de Wolski]

Welcome!

You can use randperm

doc randperm

or do what randperm() does under the hood:

[~,idx] = sort(rand(1,10))

[googo]

thanks but what do you mean by doc randperm?

[Sean de Wolski]

At the MATLAB command prompt run:

>> doc randperm

It will bring up the documentation. FYI: In this forum, gray text like that represents code to be executed.

Answer 2

[Image Analyst]

From the help:

p = randperm(n,k) returns a row vector containing k unique integers selected randomly from 1 to n inclusive.

So

x = rand(1,20) % Generate sample data.
n = 5; % Take 5 from x at random locations
% Get the random locations.
xIndexes = randperm(numel(x), n);
% Extract x from those random locations.
xSubSample = x(xIndexes)