MATLAB: How to extract the rows of a matrix when I have the row numbers stored in another vector

Question

I have a 102×3 matrix, I need to extract all the rows that have the number 1 in the first column and put them in a separate matrix.

Ive tried using the find function to produce a vector listing all the row numbers of when this occurs however I am not sure how to use this to extract the whole rows from the large matrix.

Answer 1

   A = randi([0 4],102,3);
   idx = find(A(:,1) == 1);
   B = A(idx,:);

Another way:

   B = A(A(:,1)==1,:);