How do I change the values of rows in specific columns based on another table which serves as a lookup?

Say I have two datasets loaded in Matlab. The two datasets are shown below together with the desired output (Excel screenshot is for illustration purposes only):

Let's say the first one is A.

A =

Then B should serve as the lookup table:

How do I change the values in A to the values from data B column 1 provided that the data A is equal to the data in B column 2?

Sample output should look like this:

A (values are replaced with values from B column 1) =

Answer 1

[Stephen23]

>> A = [2001,2001;2001,2003;2001,2005;2001,2006]
A =
   2001   2001
   2001   2003
   2001   2005
   2001   2006
>> B = [1,2001;2,2003;3,2004;4,2005;5,2006]
B =
      1   2001
      2   2003
      3   2004
      4   2005
      5   2006
>> [X,Y] = ismember(A,B(:,2));
>> A(X) = B(Y(X))
A =
      1      1
      1      2
      1      4
      1      5

[Alben Bagabaldo]

This worked with my actual dataset. Thank you very much!