Function message_vectors 

fn message_vectors(
    language: &FastText,
    path: &Path,
    messages: &[Message],
    threads: usize,
    progress: &mut dyn FnMut(&Progress),
    cancel: &Cancel,
) -> Result<Vec<f64>, LearnError>

Every message’s vector: the plain mean of its words’ fastText vectors, computed on threads threads, in f64, from the tokenized corpus.