[ARROW-15858] [C++][R] Can't cast integer difftime to duration (but works with double)

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Duplicate
• Component/s: C++, R
• External issue URL: https://github.com/apache/arrow/issues/31295
• Assignee: Unassigned
• Reporter: Dragoș Moldovan-Grünfeld
• Created: 07/Mar/22 14:53
• Updated: 11/Jan/23 11:40
• Resolved: 29/Jun/22 16:51

Description

It's possible to cast doubles to durations, but not integers. This has been found in the R code via the issues below:

The shortest reprex I can make is as follows:

# Successfully cast a double to a duration
vec_to_Array(as.difftime(32, units = "secs"), NULL)$cast(duration())
#> Array
#> <duration[s]>
#> [
#>   32
#> ]

# Fail to do so with an integer
vec_to_Array(as.difftime(32L, units = "secs"), NULL)$cast(duration())
#> Error: NotImplemented: Unsupported cast from int32 to duration using function cast_duration

----------------------------------------------------------------------------
I would expect both a and b to create a duration object of 32 seconds, but the second one returns an int32

library(arrow, warn.conflicts = FALSE)

a <- as.difftime(32, units = "secs") # i.e. a double
b <- as.difftime(32L, units = "secs") # i.e. an integer

Array$create(a)
#> Array
#> <duration[s]>
#> [
#>   32
#> ]
Array$create(b)
#> Array
#> <int32>
#> [
#>   32
#> ]

If I try to be explicit, I get somewhat of a clue why that might be happening:

 
Array$create(a, type = duration())
#> Array
#> <duration[s]>
#> [
#>   32
#> ]
Array$create(b, type = duration())
#> Error:
#> ! NotImplemented: Extend

Nevertheless, the fallback to creating an integer was unexpected.

Issue Links

• is superceded by: ARROW-15862 [C++] Provide a way to go from numeric to duration