Delete columns from a matrix

Hello, all. I know there are several posts about reducing matrices, but I haven't found one that answers my question. I have two matrices: class1 is 29x284214 and class2 is 29x492. I need to randomly delete columns from class1 until it has same number of columns as class2. I've tried the following code, but it's not very efficient and I'm hoping you can show me a better way.

if true
  while length(class1) > length(class2)
      index = randi(length(class1));
      class1(:,index) = [];
  end
end

I do not need to keep the original class1 matrix. Thanks for any help you can provide.

Answer 1

[David Fletcher]

diff=size(class1,2)-size(class2,2)
deletionList=randperm(size(class1,2),diff)

class1(:,deletionList)=[]

[Bill Symolon]

Perfect, thanks!