pub fn as_type(&mut self, dtype: DType) {
        let x = self.to_type(dtype);
        self.dtype = x.dtype;
        self.values = x.values;
    }
Type casting for Series

# Examples

```rust
extern crate peroxide;
use peroxide::fuga::*;

fn main() {
let mut a = Series::new(vec![1i32, 2, 3, 4]);
a.as_type(USIZE);

assert_eq!(a, Series::new(vec![1usize, 2, 3, 4]));
}
```
src/structure/dataframe.rs