adding elements to beginning of each row

I have a 3x4 array that looks like this [1,2,3,4; 5,6,7,8; 9,10,11,12]. I want to add n number of zeros (n being the row number), so that it looks like this [0,1,2,3,4,0,0; 0,0,1,2,3,4,0; 0,0,0,1,2,3,4] Is there any way to achieve this in Matlab? rows and arrays work quite differently from my programming knowledge so I'm having a little difficulty.

[Image Analyst]

So

m1 = [1,2,3,4; 5,6,7,8; 9,10,11,12] % Input
m2 = [0,1,2,3,4,0,0; 0,0,1,2,3,4,0; 0,0,0,1,2,3,4] % Desired output

gives

m1 =
     1     2     3     4
     5     6     7     8
     9    10    11    12
m2 =
     0     1     2     3     4     0     0
     0     0     1     2     3     4     0
     0     0     0     1     2     3     4

What rule are you giving for transferring some (but not all) of the elements from m1 to m2?

Have you considered circshift()?

Answer 1

[Akira Agata]

I think the desired result could be the following.

     0     1     2     3     4     0     0
     0     0     5     6     7     8     0
     0     0     0     9    10    11    12

Assuming this, the solution would be like this.

A = [1,2,3,4; 5,6,7,8; 9,10,11,12];
A1 = [A,zeros(3)];
B = splitapply(@(x,d) circshift(x,d), A1, (1:3)', (1:3)');

[Lucas Chae]

This is precisely what I needed! Thank you so much.

Answer 2

[Image Analyst]

Here's one way:

m1 = [1,2,3,4; 5,6,7,8; 9,10,11,12]
% m2 = [0,1,2,3,4,0,0; 0,0,1,2,3,4,0; 0,0,0,1,2,3,4]
rowOne = [0, m1(1,:), zeros(1, size(m1, 2)-2)]
m2 = repmat(rowOne, [size(m1, 1), 1])
for row = 1 : size(m2, 1)
  thisRow = m2(row, :)
  m2(row,:) = circshift(thisRow, row-1);
end
m2 % Show in command window.

It gives

m2 =
     0     1     2     3     4     0     0
     0     0     1     2     3     4     0
     0     0     0     1     2     3     4

just like you requested.

[Lucas Chae]

I had an error in my question, and I didn't need the modulus operator (and yet you figured out a way!). After that, your method works perfectly too, so thank you.