Extract certain rows of matrix if they have a certain number

I have a large set of data of hourly data taken over a few years. I'm trying to extract only afternoon hour data into a new matrix. Data looks like this:

M = [ 1 2011 1 0 399
      1 2011 1 2 440
      1 2011 1 3 430]

I'm trying to extract the rows that have numbers 17-21 in column 4 into a new matrix.

Answer 1

[Walter Roberson]

mask = ismember(M(:,4), 17:21);
afternoon_M = M(mask,:);

There are other ways to write the test, such as

mask = M(:,4) >= 17 & M(:,4) <= 21;

[Matthew Arenas]

Perfect! Thanks!