randomly picking from a series of elements

Hello everybody, need help to pick random elements from a series of data. Please help!

In fact I have a Matrix with three column containing 7000 lines and I want to pick only 500 lines randomly what function should I use? Thank you.

[Stalin Samuel]

give some example

Answer 1

[Roger Stafford]

To avoid repetitions you can do the following. Let M be the array with 7000 rows from which you wish to select 500 at random.

   M2 = M(randperm(7000,500),:);

If you want the rows to still be in the same order as they were in M, do this instead:

   M2 = M(sort(randperm(7000,500)),:);

Answer 2

[Guillaume]

I would use randi for this:

m = repmat((1:7000)', 1, 3); %matrix with 7000 lines, 3 columns for demo

rows = randi(size(m, 1), 1, 500); %select 500 random integers between 1 and the number of lines in m
randrows = m(rows, :); %get these rows

[Image Analyst]

Wajdi's 'Answert" moved here:

Many thanks I will try this command lines. I'd like to ask if possible to read the data from excel work sheet or how can I get my data from excel?

Wajdi, unless you're giving and answer to your original question, just add a "Comment" to the person you are replying to.

[Guillaume]

Actually, Roger is right, my answer can repeat some rows, so use (and accept) his answer.

As for the bit about excel, start a new question as it has nothing to do with the original question.