for readability and maintainability, it would be bette to split the code,
store the result of the first collect in a local variable with a meaningful name.
then on a separate line stream the results and do the needed operations

quiet late,
but in case you still need the answer:
you need to have the import statement below:

import java.util.Arrays;

you might want to have skip and map on a separate line,
this way it will be easier to read.