Rectangling data: special cases

df_unnamed_paired <- tribble(
  ~x, ~y, ~z,
  "a", list("a1", "a2"), list("A1", "A2"),
  "b", list("b1", "b2", "b3"), list("B1", "B2", "B3")
)
df_unnamed_paired

## # A tibble: 2 × 3
##   x     y          z         
##   <chr> <list>     <list>    
## 1 a     <list [2]> <list [2]>
## 2 b     <list [3]> <list [3]>