pub fn split_to_struct<'a, F, I>(
    ca: &'a ChunkedArray<Utf8Type>,
    by: &'a ChunkedArray<Utf8Type>,
    n: usize,
    op: F
) -> Result<StructChunked, PolarsError>where
    F: Fn(&'a str, &'a str) -> I,
    I: Iterator<Item = &'a str>,
Available on crate feature dtype-struct only.