Selecting random points from data file

Hi, is there any algorethim to select random points from a large data file. Lets say I want to select data after every 20 values. x = [1:0.1:1000]

If I want y = select every 10th 20th or 50th point of x

Thanks Amb

[per isakson]

Try

    >> M = 1:100;
    M(20:20:100)
    ans =
        20    40    60    80   100

but that's hardly random.

[Azzi Abdelmalek]

The question is not clear, "10th 20th or 50th point of x"

[amberly hadden]

Sorry if its not clear I mean to write pick every 10th or 20th point of x.

Amb

[amberly hadden]

sorry random means scanig rando area up down lesft right

Answer 1

[Mohammad Abouali]

x = [1:0.1:1000];

x_every10th=x(10:10:numel(x));

x_every20th=x(20:20:numel(x));

x_every50th=x(50:50:numel(x));

You get the idea.

[amberly hadden]

Thanks but its out put is 1*2 matix. Quit differnt from what I want

here is an example lets say x = a b c (3*2000 Matrix) I want to pick every 10th value of x means I need to output x = a10 b10 c10:a20 b20 c20 and so on for means pick every 10th value

[Mohammad Abouali]

So you are changing the question. In your question x is a row vector now it is matrix. and you want every 10th, 20th, ... row

then change it to this:

x_every10th=x(10:10:size(x,1),:);
x_every20th=x(20:20:size(x,1),:);
x_every50th=x(50:50:size(x,1),:);

[amberly hadden]

yeah I have a 307000*3 matrix

want to select every 10th row. Is there any wany to data from random rows lets say for region I'm more interested I can select every 20th point for region Im not much interested slect every 50th and close to my sourse select every 10th point.

Thanks much apriciated

[amberly hadden]

another thing I want out put in 3 columns its just producing one column.

Answer 2

[Azzi Abdelmalek]

x = [1:0.1:1000];
n=randi(5)*10   
out=x(n:n:end)

[amberly hadden]

randi is good option but how would I aviod repeation

Thanks