[jira] [Updated] (ARROW-17606) [C++] Cast float to decimal truncates

["Kouhei Sutou (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-17606?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kouhei Sutou updated ARROW-17606:
---------------------------------
    Fix Version/s: 11.0.0
                       (was: 10.0.0)

> [C++] Cast float to decimal truncates
> -------------------------------------
>
>                 Key: ARROW-17606
>                 URL: https://issues.apache.org/jira/browse/ARROW-17606
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: C++
>            Reporter: Neal Richardson
>            Priority: Major
>             Fix For: 11.0.0
>
>
> Even with all of the cast options to allow truncation and overflow set to False, cast from double to decimal truncates. 
> Short reproducer in R:
> {code}
> library(arrow, warn.conflicts = FALSE)
> a <- Scalar$create(sqrt(2))
> a
> #> Scalar
> #> 1.4142135623730951
> a$cast(decimal(5, 1))
> #> Scalar
> #> 1.4
> {code}
> Longer version that shows the cast options:
> {code}
> library(arrow, warn.conflicts = FALSE)
> library(dplyr, warn.conflicts = FALSE)
> tab <- arrow_table(a = sqrt(2))
> tab
> #> Table
> #> 1 rows x 1 columns
> #> $a <double>
> tab$a
> #> ChunkedArray
> #> <double>
> #> [
> #>   [
> #>     1.4142135623730951
> #>   ]
> #> ]
> # See that all of the cast options are false:
> tab %>% 
>   mutate(b = cast(a, decimal(5, 1)))
> #> Table (query)
> #> a: double
> #> b: decimal128(5, 1) (cast(a, {to_type=decimal128(5, 1), allow_int_overflow=false, allow_time_truncate=false, allow_time_overflow=false, allow_decimal_truncate=false, allow_float_truncate=false, allow_invalid_utf8=false}))
> #> 
> #> See $.data for the source Arrow object
> new_tab <- tab %>% 
>   mutate(b = cast(a, decimal(5, 1))) %>% 
>   compute()
> new_tab
> #> Table
> #> 1 rows x 2 columns
> #> $a <double>
> #> $b <decimal128(5, 1)>
> new_tab$b
> #> ChunkedArray
> #> <decimal128(5, 1)>
> #> [
> #>   [
> #>     1.4
> #>   ]
> #> ]
> {code}



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