how to exract varying matrix data

I have a file X=(20,350) and i want to select the column value using a selecting a selcting matrix y= (1,350)

for i= 1:350
p(y(i),:)= X(1:y(i),:) 
 end

but couldn't solve the problem . any help in this regard is highly appreciated.

Answer 1

[Iain]

 p(y(i),:)= X(1:y(i),:)

Is trying to put a y(i) by "n" matrix into a 1 by "n" matrix, which CANNOT work.

 p(y(i),:)= X(y(i),:)

Is trying to put a 1 by "n" matrix into a 1 by "n" matrix, which can work, provided that "y" has enough elements.

If you define y to be a list of the ROWS you want (this is the way round you've got your code, swap the :, and y(i) round for columns):

 p = zeros(size(X)); % or ones, or NaNs, or whatever else as needed.
 y = [1 5 7 8 9 350];
 for i = 1:numel(y)
  p(y(i),:) = X(y(i),:);
 end

[Ede gerlderlands]

thanks