when you have groups of columns

when you have groups of columns that you want to compute with simultaneously.

iteration.qmd

@@ -393,7 +393,27 @@ df_long |>
  summarize(mean = weighted.mean(val, wts))
 ```
 
-If needed, you could `pivot_wider()` this back to the original form.
+If needed, you could `pivot_wider()` this back to the original form. 
+
+This problem was actually solved on StackOverflow much earlier to release of 2nd edition.
+
+```{r}
+df_paired |>
+ summarise(
+ across(
+ .cols = ends_with("val"),
+ .fns = ~ weighted.mean(., get(str_replace(
+ cur_column(), "val", "wts"
+ ))),
+ .names = '{str_remove(col, "_val")}'
+ )
+ )
+
+#> # A tibble: 1 × 4
+#> a b c d
+#> <dbl> <dbl> <dbl> <dbl>
+#> 1 0.180 0.199 -0.208 -0.746
+```
 
 ### Exercises