finding index of several values within a vector efficiently

I am trying to find the index of 'several' values within an array/vector. For instance, I have a vector [1 2 5] and matrix X=[1 5 4 3 2]. I want it to return [1 5 2]. I could write a for loop that finds each values in that vector such as find(X==1), then find(X==2) ..., but I was hoping there is a vectorized way to do this. Thanks.

Answer 1

[the cyclist]

v = [1 2 5];
X = [1 5 4 3 2];

[tf loc] = ismember(v,X);

"loc" is the vector you want.

Answer 2

[Matt Fig]

idx = [1 2 5];
X = [1 5 4 3 2];

vals = X(idx)  % linear indexing.

[the cyclist]

If I am interpreting Jimmian's question correctly, this method only gives the correct answer to the example because of a numerical coincidence. For example, if

X = [0 0 0 0 0 1 5 4 3 2]

then I think he wants the output to be

loc = [6 10 7]

and not

[0 0 0].

[Matt Fig]

Exactly how I interpreted your answer when I read it (works because of a coincidence).

:-)

It would be nice to have an example from OP that is unambiguous......