Replace value-by-value WITHOUT a loop, from 2 vectors?

Dear all!

I want replacing the value of the element in vector a with the corresponding value of the element in vector b. Therefore, I have coded like this:

function result=Replace_Value_by_Value(X,a,b)
% Replace the value of the element in vector a 
% by the corresponding value of the element in vector b
%length(a) = length(b)
%length(X)>>> length(a)
result=X;
    for i=1:size(X,1)
        for j = 1:length(a)
            if X(i)==a(j) 
                result(i)=b(j);
            end
        end
    end
end

Example:

X=[1,2,3,4;5,6,7,8;1,4,2,1;6,7,1,2]
a=[1,2,3,4]
b=[100,200,500,400]

Result must be:

result =

100 200 500 400

5 6 7 8

100 400 200 100

6 7 100 200

Is there any other way without using FOR?

Please help. Thank you..

[madhan ravi]

Illustrate with an example of your input and the desired output.

[Nguyen Anh Cuong]

Example:

X=[1,2,3,4;5,6,7,8;1,4,2,1;6,7,1,2]
a=[1,2,3,4];
b=[100,200,500,400];
result=Replace_Value_by_Value(X,a,b)

Result must be:

X =

1 2 3 4

5 6 7 8

1 4 2 1

6 7 1 2

result =

100 200 500 400

5 6 7 8

100 400 200 100

6 7 100 200

Answer 1

[Jan]

X = [1,2,3,4;5,6,7,8;1,4,2,1;6,7,1,2];
a = [1,2,3,4];
b = [100,200,500,400];

[M, ia] = ismember(X, a);
X(M)    = b(ia(M))