Extracting elements from a matrix

Hello,

I have a column matrix A with 50 elements and a small column matrix B with 5 elements. I would like to determine the values of the 5 indices i of A for which the value of A(i) is equal to one of the 5 elements of B.

Then there is a column matrix C with 50 elements and I would like to extract all elements of C for the indices determined above in a new matrix D (of 5 elements).

Can someone show me a good way to perform these operations?

I tried to set up a for-loop to go through every single element of A but I don't know how to express that A(i) should be equal to any of the elements of B (in the nested if-loop). Also I am not sure of the best is to save the obtained indices in a new matrix for extracting elements from C.

Many thanks!

[KSSV]

Read about ismember.

Answer 1

[KSSV]

% Random data for demo 
A = rand(50,1) ;
B = A(randperm(50,5)') ;   % select five elements of A randomly 
C = rand(50,1) ; 

[c,ia] = ismember(A,B) ;   % get the indices of B in A 

D = C(c) ; 

[Lenilein]

Thank you, it was very helpful!

From what I read in documentation, the answer in your example should be:

[c,ia] = ismember(B,A) ; % get the indices of B in A

D = C(ia) ;