extracting data from matrix

Hello every bod

let assume matrix

A =
 [10 20 1
 30 40  2
 50 60  3
 70 80  4
 90 100 5] 

B = 
[30 40
 70 80]

we need to identify the third column of the matrix B, hence

B =
[30 40  2
 70 80  4]

Answer 1

[Azzi Abdelmalek]

A= [10 20 1
  30 40  2
  50 60  3
  70 80  4
  90 100 5]
B=[30 40
  70 80]
idx=ismember(A(:,1:2),B,'rows')
B(:,3)=A(idx,3)

[Abdelwahab Fawzy]

I tried this code for other different matrices I get a problem at which the third column is not compatible with the first and 2'nd column data in terms of ordering

[Azzi Abdelmalek]

Can you explain? post an example to make your question clear