MATLAB: Does available funtion in Matlab can extract rows satisfied a condition

Question

I want to create a matrix has rows has first column value = 4 from matrix a; like

Does available funtion in Matlab can extract rows satisfied a condition? Thanks so much!

Answer 1

Read about array indexing: https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html and https://www.mathworks.com/help/matlab/math/array-indexing.html

a = [4 5 6;
     4 5 6;
     5 5 6];
 
idx = a(:,1)==4;
b = a(idx, :);