How do you return the value of one vector at specified value of another vector

I want to return the value of a vector A at the specified value of vector B.

So, when vector B = 805, I'd like code to return the value of vector A.

They're the same length.

Answer 1

[Matt J]

It's not entirely clear what you mean. Possibly, you want this

A(B==805)

or you could mean,

 A(B)

[balsip]

Thank you for your input.

My apologies. I thought that your first answer might work (it creates an empty matrix). Let me see if I can rephrase it better.

I want to return the value (i.e., not index) of A when the value of B (i.e., not index) is 805.

[Matt J]

Then the first answer should have worked. Clearly, your B vector does not contain any occurrence B(i)==805, or at least not exactly. You may need a floating point tolerance.

[Guillaume]

A(ismembertol(B, 805))

may fix the problem with the value in B not being exactly equal to 805 (due to floating point calculations)

Or if all the values in B are supposed to be integer:

A(round(B) == 805)

Answer 2

[John D'Errico]

Why have you not tried the obvious? What does

A(B)

provide?

It appears that you need to spend time reading the getting started tutorials for MATLAB if you do not understand how to use an index.