[jira] [Commented] (ARROW-15862) [C++] Provide a way to go from numeric to duration

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-15862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17506864#comment-17506864 ] 

Joris Van den Bossche commented on ARROW-15862:
-----------------------------------------------

bq.   Would it make sense to support float -> duration or int32 -> duration? 

Do you mean in the (C++) Cast machinery? 

We also don't support this for example timestamp:

{code:python}
# casting int64 to timestamp is fine
>>> pa.array([1, 2, 3]).cast(pa.timestamp("s"))
<pyarrow.lib.TimestampArray object at 0x7fb5c314c340>
[
  1970-01-01 00:00:01,
  1970-01-01 00:00:02,
  1970-01-01 00:00:03
]

# casting int32 not
>>> pa.array([1, 2, 3], type="int32").cast(pa.timestamp("s"))
... ArrowNotImplementedError: Unsupported cast from int32 to timestamp using function cast_timestamp
../src/arrow/compute/function.cc:231  DispatchBest(&inputs)
{code}

We might want to do this, but I think it is a general issue / question for the casting machinery of Arrow how to handle casts that might need an additional step (like "int32 -> timestamp" can be done as "int32 -> int64 -> timestamp" which are all supported)

> [C++] Provide a way to go from numeric to duration
> --------------------------------------------------
>
>                 Key: ARROW-15862
>                 URL: https://issues.apache.org/jira/browse/ARROW-15862
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Dragoș Moldovan-Grünfeld
>            Priority: Critical
>
> *Update*: I keep forgetting that R integers are translated into int32 (since R does not have int64). int64 -> duration is supported. 
>  Would it make sense to support float -> duration or int32 -> duration? 
> ======================
> Currently it is not possible to directly create a duration object from a numeric one (for example through casting).
> {code:r}
> library(arrow)
> a <- Array$create(32L)
> a$cast(duration("s"))
> #> Error: NotImplemented: Unsupported cast from int32 to duration using function cast_duration
> #> /Users/dragos/Documents/arrow/cpp/src/arrow/compute/function.cc:231  DispatchBest(&inputs)
> {code}
> This underpins a lot of the date-time arithmetic in R, which support the conversion/ coercion of an integer to difftime (R's equivalent for duration), such as in the pipeline below.
> {code:r}
> library(arrow, warn.conflicts = FALSE)
> #> See arrow_info() for available features
> library(dplyr, warn.conflicts = FALSE)
> library(lubridate, warn.conflicts = FALSE)
> df <- tibble(time = as_datetime(c("2022-03-07 15:00:28", "2022-03-06 14:00:28"))) 
> df
> #> # A tibble: 2 × 1
> #>   time               
> #>   <dttm>             
> #> 1 2022-03-07 15:00:28
> #> 2 2022-03-06 14:00:28
> df %>% 
>   mutate(time2 = time + seconds(2))
> #> # A tibble: 2 × 2
> #>   time                time2              
> #>   <dttm>              <dttm>             
> #> 1 2022-03-07 15:00:28 2022-03-07 15:00:30
> #> 2 2022-03-06 14:00:28 2022-03-06 14:00:30
> {code}



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