Function std::slice::unzip
pub fn unzip<T, U, V: Iterator<(T, U)>>(iter: V) -> (~[T], ~[U])
Convert an iterator of pairs into a pair of vectors.
Returns a tuple containing two vectors where the i-th element of the first vector contains the first element of the i-th tuple of the input iterator, and the i-th element of the second vector contains the second element of the i-th tuple of the input iterator.