How to take only few rows in a large matrix

Dear All,

I'm working with a large amount of data in a matrix.My problem is the following one.

I have a large matrix which looks like:

• Initial matrix

X Y Z

0.2 0 6

0.4 0 7

0.6 0 8 values of Y are repeated a lot of time

.. .. ..

.. .. ..

0.1 2 9

0.4 2 10

0.8 2 11

.. .. ..

11 4 6

12 4 8

4 4 9

• Final marix

X Y Z

0.2 0 6

0.1 2 9

11 4 6

My goal is to take few rows of the matrix because Y values are repeated.

[Image Analyst]

Which row do you want to take? The first row when that value of Y appears? Are y always integers or can they be fractional?

Answer 1

[A Jenkins]

You can use the function unique()

[C,IA,IC]=unique(A(:,2))
A(IA,:)

Or perhaps if you already know the indicies of the rows you want, you can select them row-wise:

idxIwant=[1 3 9]
C=A(idxIwant,:);

[afrya]

Thanks for your answer but I don't know the indices of the rows, the matrix that I'm working with has 700 000 rows. I'll do it with the function unique