Function train_test_split 

pub fn train_test_split<X, Y>(
    x: &Array2<X>,
    y: &Array1<Y>,
    test_size: f64,
    random_state: Option<u64>,
) -> Result<(Array2<X>, Array2<X>, Array1<Y>, Array1<Y>)>
where
    X: Clone,
    Y: Clone,

Split arrays or matrices into random train and test subsets