how to filter data based on one value in a column?

how to filter data based on one value in a column. i have 40000 rows and 4 columns. in 4th column i have values 1, 2, 3, 4. i want to filter all records in which the values of the 4th column should only be 3. the data is 40000 X 4 double type.

Answer 1

[Cris LaPierre]

use a logical array (Ch 12 in MATLAB Onramp).

A = rand(10,3);
A(:,4) = randi(4,10,1)

A = 10×4

0.7596 0.0937 0.1802 3.0000 0.1846 0.3415 0.3006 4.0000 0.2324 0.8903 0.4734 4.0000 0.8114 0.1004 0.7153 3.0000 0.5624 0.9496 0.5770 1.0000 0.3444 0.0529 0.0754 2.0000 0.1635 0.0971 0.6925 1.0000 0.6909 0.6383 0.7955 3.0000 0.5133 0.3658 0.8523 2.0000 0.1696 0.2123 0.9565 2.0000

idx = A(:,4)==3;
B = A(idx,:)

B = 3×4

0.7596 0.0937 0.1802 3.0000 0.8114 0.1004 0.7153 3.0000 0.6909 0.6383 0.7955 3.0000