Can I store row numbers of a matrix in a column without using any loop?

How will I store the first column of a matrix as its corresponding row number without using a loop. That is, the first column for a 3x3 matrix as [1 . .;2 . .;3 . .].

[Aquatris]

You mean something like this;

A=[1 5 6; 2 7 8;3 9 0];
B = A(:,1); % this will make B = [1;2;3]

[Nagesh A P]

Ok. This is the case. I have a very large data, something like 100,000 data points, so 100,000 rows. I want to store the first column of a matrix newly created (with as many rows as number of data points mentioned) as its corresponding row number. I can do what you've mentioned. But it'll take me a new matrix and another loop to create that matrix. Could you suggest something which takes less time.

Answer 1

[Nithin Banka]

a = magic(3);
a(:, 1) = [1:3]; % This will store the row index in the first column of 'a'

[Guillaume]

The [] brackets around 1:3 are completely unnecessary and only slow the code down. A good answer wouldn't hardcode the height of the matrix:

a(:, 1) = 1:size(a, 1);

If that is indeed what is required.

[Nagesh A P]

Thad did save my time bro. thanks

[Nagesh A P]

Thanks @nithin and @Guillaume