[jira] [Commented] (ARROW-16007) [R] binding for grepl has different behaviour with NA compared to R base grepl

["Andy Teucher (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-16007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17510837#comment-17510837 ] 

Andy Teucher commented on ARROW-16007:
--------------------------------------

I meant to add - whether you'd like to change the behaviour or document the differences, I'd be keen to take it on!

> [R] binding for grepl has different behaviour with NA compared to R base grepl
> ------------------------------------------------------------------------------
>
>                 Key: ARROW-16007
>                 URL: https://issues.apache.org/jira/browse/ARROW-16007
>             Project: Apache Arrow
>          Issue Type: Improvement
>    Affects Versions: 7.0.0
>            Reporter: Andy Teucher
>            Priority: Minor
>
> The arrow binding to {{grepl}} behaves slightly differently than the base R {{{}grepl{}}}, in that it returns {{NA}} for {{NA}} inputs, whereas base {{grepl}} returns {{{}FALSE with \{{NA}}inputs. arrow's implementention is consistent with stringr::str_detect(){}}}, and both {{str_detect()}} and {{grepl()}} are bound to {{match_substring_regex}} and {{match_substring}} in arrow.
> I don't know if this is something you would want to change so that the {{grepl}} behaviour aligns with base {{{}grepl{}}}, or simply document this difference?
> Reprex:
>  
> {code:r}
> library(arrow, warn.conflicts = FALSE, quietly = TRUE)
> library(dplyr, warn.conflicts = FALSE, quietly = TRUE)
> library(stringr, quietly = TRUE)
> alpha_df <- data.frame(alpha = c("alpha", "bet", NA_character_))
> alpha_dataset <- InMemoryDataset$create(alpha_df)
> mutate(alpha_df, 
>        grepl_is_a = grepl("a", alpha), 
>        stringr_is_a = str_detect(alpha, "a"))
> #>   alpha grepl_is_a stringr_is_a
> #> 1 alpha       TRUE         TRUE
> #> 2   bet      FALSE        FALSE
> #> 3  <NA>      FALSE           NA
> mutate(alpha_dataset, 
>        grepl_is_a = grepl("a", alpha), 
>        stringr_is_a = str_detect(alpha, "a")) |> 
>   collect()
> #>   alpha grepl_is_a stringr_is_a
> #> 1 alpha       TRUE         TRUE
> #> 2   bet      FALSE        FALSE
> #> 3  <NA>         NA           NA
> # base R grepl returns FALSE for NA
> grepl("a", alpha_df$alpha) # bound to arrow_match_substring_regex
> #> [1]  TRUE FALSE FALSE
> grepl("a", alpha_df$alpha, fixed = TRUE) # bound to arrow_match_substring
> #> [1]  TRUE FALSE FALSE
> # stringr::str_dectect returns NA for NA
> str_detect(alpha_df$alpha, "a")
> #> [1]  TRUE FALSE    NA
> alpha_array <- Array$create(alpha_df$alpha)
> # arrow functions return null for null (NA)
> call_function("match_substring_regex", alpha_array, options = list(pattern = "a"))
> #> Array
> #> <bool>
> #> [
> #>   true,
> #>   false,
> #>   null
> #> ]
> call_function("match_substring", alpha_array, options = list(pattern = "a"))
> #> Array
> #> <bool>
> #> [
> #>   true,
> #>   false,
> #>   null
> #> ]
> {code}
>  
>  



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