How to select rows in a matrix with a for loop?

I have a 3061x107 matrix. I want to reduce it to a 817x107 matrix. My current code currently saves what I want as a new matrix into a very large column so its 87000x1.

My current code:

density=[];
for i=1:length(densityt)
    dcol=densityt(:,i);
    dcol=dcol(1:817,:);
    density=[density;dcol];
end 

Answer 1

[Ameer Hamza]

Following code is more efficient and outputs what you want

density = densityt(1:817, :)