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https://issues.apache.org/jira/browse/ARROW-16007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17511971#comment-17511971
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Jonathan Keane commented on ARROW-16007:
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You've definitely identified the two paths for this. I agree with your
hesitance that empty string and nulls shouldn't be conflated.
The string conversion from R is a bit complicated, but
https://github.com/apache/arrow/blob/ddb663b1724034f64cc53d62bd2d5a4e8fa42954/r/src/r_to_arrow.cpp#L777-L824
(and the rest of that file) is a good starting point.
All of that being said, I would probably go the second route you mention (and
sorry for not responding with this earlier!):
> but then it occurred to me that if this is just a special case in R, maybe
> it's better to do it on the R side and just change NA to FALSE in the return
> value of the binding of grepl?
You could put a call to {{if_else}} + {{is.na}} bindings inside of the
{{grepl}} binding and get the behavior in R. We do have some support via
options for different null handling behaviors for other functions, but I
suspect R is a bit of an outlier here (I tried to construct a reprex in Python
to see if I could see what it does, but every `re.match()` with anything
missing-like is a type error!).
> [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 implementation 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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