[GitHub] [arrow] eitsupi commented on a diff in pull request #35702: [R][Documentation] Document workaround for window-like functionality

["eitsupi (via GitHub)" <gi...@apache.org>]

eitsupi commented on code in PR #35702:
URL: https://github.com/apache/arrow/pull/35702#discussion_r1200622342


##########
r/vignettes/data_wrangling.Rmd:
##########
@@ -165,6 +165,34 @@ sw2 %>%
   transmute(name, height, mass, res = residuals(lm(mass ~ height)))
 ```
 
+Because window functions are not supported, computing an aggregation like `mean()` on a grouped table or within a rowwise opertation like `filter()`  is not supported:
+
+```{r}
+sw %>%
+  select(1:4) %>%
+  filter(!is.na(hair_color)) %>%
+  group_by(hair_color) %>%
+  filter(height < mean(height, na.rm = TRUE))
+```
+
+This operation can be accomplished in arrow by computing the aggregation separately, for example within a join operation: 
+
+```{r}
+
+sw %>%  
+  select(1:4) %>%
+  filter(!is.na(hair_color)) %>%
+  left_join(sw %>% 
+    group_by(hair_color) %>%
+    summarize(mean_height = mean(height, na.rm = TRUE)) 
+    ) %>%
+  filter(height < mean_height) %>% 
+  select(-mean_height) %>%
+  collect()
+

Review Comment:
   How about formatting it as follows?
   
   ```suggestion
   sw %>%
     select(1:4) %>%
     filter(!is.na(hair_color)) %>%
     left_join(
       sw %>% 
         group_by(hair_color) %>%
         summarize(mean_height = mean(height, na.rm = TRUE)) 
       ) %>%
     filter(height < mean_height) %>% 
     select(!mean_height) %>%
     collect()
   ```



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