Delete specific periodic rows or columns in matrix

Hei! I have a big matrix and I need to delete specific columns. More specifically, I have 2250 columns consisting of 50 subsets of 45 columns. In each subset, I need to keep the first 18 columns, delete columns 19 and 20, keep columns 21 to 45 and so on. In the end i will have deleted 2 columns in every set, so I have 2150 columns in total. Any help would be really appreciated!

Answer 1

[KSSV]

M = rand(2250) ; % random data 
idx = [19 20 21 45] ;   % columns to delete/ remove 
M(:,idx) =[];  % removing those columns

[Stergiani]

Hei Doesn't this just keep in the matrix the columns you define?

[KSSV]

You are right, edited it.