how to change datetime series to date series? - rust

Question

let datetime = frame.column("datetime_nano")?.cast(&DataType::Datetime(TimeUnit::Nanoseconds, None))?;
let date = datetime.cast(&DataType::Date)?;
let time = datetime.cast(&DataType::Time)?;
println!("{}", datetime);
println!("{}", date);
The date part display between date and datetime is not equal. Is there any way to get the correct date series ?
I have read the datetime.date() function. just only solve dtype == DateType::Date.
#[cfg(feature = "dtype-date")]
pub fn date(&self) -> PolarsResult<&DateChunked> {
match self.dtype() {
DataType::Date => unsafe {
Ok(&*(self.as_ref() as *const dyn SeriesTrait as *const DateChunked))
},
dt => Err(PolarsError::SchemaMisMatch(
format!("Series of dtype: {dt:?} != Date").into(),
)),
}
}

Answer 1

The polars tests are a good place to look for code examples.
It looks like you're asking about .strptime which will create a Datetime from a string.
Once you have a Datetime - you can .cast to Date / Time objects.
use polars::prelude::*;
fn main() -> PolarsResult<()> {
let frame = df!("datetime_nano" => ["2019-03-22T14:00:01.700311864"])?
.lazy()
.with_column(col("datetime_nano").str().strptime(StrpTimeOptions {
date_dtype: DataType::Datetime(TimeUnit::Nanoseconds, None),
..Default::default()
}))
.collect()?;
let datetime = frame.column("datetime_nano")?;
let date = datetime.cast(&DataType::Date)?;
let time = datetime.cast(&DataType::Time)?;
println!("{:?}", frame);
println!("{:?}", datetime);
println!("{:?}", date);
println!("{:?}", time);
Ok(())
}
shape: (1, 1)
┌───────────────────────────────┐
│ datetime_nano │
│ --- │
│ datetime[ns] │
╞═══════════════════════════════╡
│ 2019-03-22 14:00:01.700311864 │
└───────────────────────────────┘
shape: (1,)
Series: 'datetime_nano' [datetime[ns]]
[
2019-03-22 14:00:01.700311864
]
shape: (1,)
Series: 'datetime_nano' [date]
[
2019-03-22
]
shape: (1,)
Series: 'datetime_nano' [time]
[
14:00:01.700311864
]