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Ranking a list of poker hands can be considered a sorting problem.
Rust provides the sort method for Vec<T> where T: Ord.
Ord types form a total order: exactly one of a < b, a == b, or a > b must be true.
Poker hands do not conform to a total order: it is possible for two hands to be non-equal but have equal sort order. Example: "3S 4S 5D 6H JH", "3H 4H 5C 6C JD".
Rust provides the PartialOrd trait to handle the case of sortable things which do not have a total order. However, it doesn't provide a standard sort method for Vec<T> where T: PartialOrd. The standard idiom to sort a vector in this case is your_vec.sort_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::{Less|Equal|Greater}));, depending on your needs.
You might consider implementing a type representing a poker hand which implements PartialOrd.