bjchambers commented on issue #527:
URL: https://github.com/apache/arrow-rs/issues/527#issuecomment-885250399
I don't think that entirely works for two reasons -- first, there are
actually multiple `Duration` types (in Rust) for the same `DataType`. Second,
the delta may also be an interval. Specifically, it needs to be constrained in
a way that supports the following arrays:
* `PrimitiveArray<DurationSecondType>` - add a fixed number of seconds
* `PrimitiveArray<DurationMicrosecondType>` - add a fixed number of
microseconds
* `PrimitiveArray<DurationMillisecondType>` - add a fixed number of
milliseconds
* `PrimitiveArray<DurationNanosecondType>` - add a fixed number of
nanoseconds
* `PrimitiveArray<IntervalDayTimeType>` - add a number of calendar days (and
seconds) (description says this is a pair of i32 packed into an i64)
* `PrimitiveArray<IntervalYearMonthType>` - add a number of calendar months
From an implementation, I think we can do this using `chrono` and
`chronoutil`. Something like:
```
pub trait ArrowTimeDelta: ArrowPrimitiveType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime;
}
impl ArrowTimeDelta<RelativeDuration> for IntervalDayTimeType {
fn get_delta(value: Self::Native) -> RelativeDuration {
// DayTime is represented as a 64 bit value -- 32 bit day and 32 bit
seconds.
let days = RelativeDuration::days(value >> 32);
let seconds = RelativeDuration::seconds((value as i32) as i64);
days + seconds
}
}
impl ArrowTimeDelta for IntervalYearMonthType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime {
// YearMonth is represented as a 32 bit value containing the number
of months.
time + RelativeDuration::months(value)
}
}
impl ArrowTimeDelta for DurationSecondType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime {
time + Duration::seconds(value)
}
}
impl ArrowTimeDelta for DurationMillisecondType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime {
time + Duration::milliseconds(value)
}
}
impl ArrowTimeDelta for DurationMicrosecondType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime {
time + Duration::microseconds(value)
}
}
impl ArrowTimeDelta for DurationNanosecondType {
fn add_to(time: NaiveDateTime, value: Self::Native) -> NaiveDateTime {
time + Duration::nanoseconds(value)
}
}
```
Then the implementation is basically iterating over a pair of arrays and
callling `add_to`.
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