# How to return values mapped to a variable?

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ekagra gupta on 25 Jun 2022
Answered: Soufian MELLAHI on 25 Jun 2022
Hello,
I have two vectors
a = [1 2 3 4 5 6 7 8 9 10]
b = [4 5 12 45 21 52 69 10 22 0]
and
a_temp = isprime(a)
How can I get values of "b" corresponding to "a_temp"?
Soufian MELLAHI on 25 Jun 2022
Edited: Soufian MELLAHI on 25 Jun 2022
Hello, (I modify my answer) you can just search/find indexes based on values of a_prime by using the following indexation method :
a_prime_val=a(a_prime); c=b(b==a_prime_val(:)); % you will get a vector of the occurences of a_prime_val within b.

Soufian MELLAHI on 25 Jun 2022
Hello, (I modify my answer) you can just search/find indexes based on values of a_prime by using the following indexation method : a_prime_val=a(a_prime); c=b(b==a_prime_val(:)); % you will get a vector of the occurences of a_prime_val within b. i hope it answers your questions.

Dyuman Joshi on 25 Jun 2022
Edited: Dyuman Joshi on 25 Jun 2022
Not sure what you want exaclty
a = [1 2 3 4 5 6 7 8 9 10];
b = [4 5 12 45 21 52 69 10 22 0];
a_temp = isprime(a)
a_temp = 1×10 logical array
0 1 1 0 1 0 1 0 0 0
b_temp = b(a_temp)
b_temp = 1×4
5 12 21 69
Soufian MELLAHI on 25 Jun 2022
Your answer provides values in b bases on prime numbers indexes in a but no equivalent with occurences of the same prime numbers in b. It depends on the real need. If he needs the prime numbers as same as present in b which is more logical. we need to remap the indexes as i have done in my answer. Otherwise your answer seems fitting.
Image Analyst on 25 Jun 2022
@Soufian MELLAHI he gave him exactly what he asked for. But we all know that what a poster asks for is not always what they mean. If it's not what he intended, then perhaps the original poster can clarify what's needed. And say if it's homework or not.
By the way, can you transfer your Answer from the above comment section to down here in the official Answer section so you might get credit for it if he accepts your answer? Thanks in advance. 🙂