[GitHub] [arrow] boshek commented on a diff in pull request #13641: ARROW-12693: [R] add unique() methods for ArrowTabular, datasets

[GitBox <gi...@apache.org>]

boshek commented on code in PR #13641:
URL: https://github.com/apache/arrow/pull/13641#discussion_r927973046


##########
r/R/dplyr.R:
##########
@@ -184,6 +184,29 @@ dim.arrow_dplyr_query <- function(x) {
   c(rows, cols)
 }
 
+#' @export
+unique.arrow_dplyr_query <- function(x, incomparables = FALSE, fromLast = FALSE, ...) {
+
+  if (incomparables == TRUE) {
+    arrow_not_supported("`unique()` with `incomparables = TRUE`")
+  }
+
+  if (fromLast == TRUE) {
+    arrow_not_supported("`unique()` with `fromLast = TRUE`")
+  }
+
+  x <- dplyr::distinct(x)
+  dplyr::collect(x)

Review Comment:
   It comes [this](https://issues.apache.org/jira/browse/ARROW-12693?focusedCommentId=17568169&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17568169) here. I think it is a bit of a grey area. My thinking was that base don't fall into the lazy dbplyr paradigm but then I remember `head`. dbplyr does not have `unique` so I don't think there is a precedent:
   
   ``` r
   library(arrow, warn.conflicts = FALSE)
   library(dplyr, warn.conflicts = FALSE)
   
   arrow_iris <- arrow_table(iris)
   duckdb_iris <- to_duckdb(arrow_iris)
   
   ## head
   head(arrow_iris)
   #> Table
   #> 6 rows x 5 columns
   #> $Sepal.Length <double>
   #> $Sepal.Width <double>
   #> $Petal.Length <double>
   #> $Petal.Width <double>
   #> $Species <dictionary<values=string, indices=int8>>
   #> 
   #> See $metadata for additional Schema metadata
   head(duckdb_iris)
   #> # Source:   SQL [6 x 5]
   #> # Database: DuckDB 0.3.5-dev1410 [root@Darwin 21.6.0:R 4.2.1/:memory:]
   #>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
   #>          <dbl>       <dbl>        <dbl>       <dbl> <chr>  
   #> 1          5.1         3.5          1.4         0.2 setosa 
   #> 2          4.9         3            1.4         0.2 setosa 
   #> 3          4.7         3.2          1.3         0.2 setosa 
   #> 4          4.6         3.1          1.5         0.2 setosa 
   #> 5          5           3.6          1.4         0.2 setosa 
   #> 6          5.4         3.9          1.7         0.4 setosa
   
   ## distinct
   distinct(arrow_iris)
   #> Table (query)
   #> Sepal.Length: double
   #> Sepal.Width: double
   #> Petal.Length: double
   #> Petal.Width: double
   #> Species: dictionary<values=string, indices=int8>
   #> 
   #> See $.data for the source Arrow object
   distinct(duckdb_iris)
   #> # Source:   SQL [?? x 5]
   #> # Database: DuckDB 0.3.5-dev1410 [root@Darwin 21.6.0:R 4.2.1/:memory:]
   #>    Sepal.Length Sepal.Width Petal.Length Petal.Width Species
   #>           <dbl>       <dbl>        <dbl>       <dbl> <chr>  
   #>  1          5.1         3.5          1.4         0.2 setosa 
   #>  2          4.9         3            1.4         0.2 setosa 
   #>  3          4.7         3.2          1.3         0.2 setosa 
   #>  4          4.6         3.1          1.5         0.2 setosa 
   #>  5          5           3.6          1.4         0.2 setosa 
   #>  6          5.4         3.9          1.7         0.4 setosa 
   #>  7          4.6         3.4          1.4         0.3 setosa 
   #>  8          5           3.4          1.5         0.2 setosa 
   #>  9          4.4         2.9          1.4         0.2 setosa 
   #> 10          4.9         3.1          1.5         0.1 setosa 
   #> # … with more rows
   #> # ℹ Use `print(n = ...)` to see more rows
   
   ##
   unique(duckdb_iris)
   #> [[1]]
   #> src:  DuckDB 0.3.5-dev1410 [root@Darwin 21.6.0:R 4.2.1/:memory:]
   #> tbls:
   #> 
   #> [[2]]
   #> From: arrow_001
   #> <Table: arrow_001>
   ```
   
   I don't think users will have an expectation here so we are probably free to decide. 



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