issues making splines with single row data frames

[topepo]

First seen in tidymodels/TMwR#367

library(tidymodels)

tidymodels_prefer()
theme_set(theme_bw())
options(pillar.advice = FALSE, pillar.min_title_chars = Inf)

ns_rec <- 
  recipe(mpg ~ ., data = mtcars) %>% 
  step_ns(disp, deg_free = 3) %>% 
  prep()

bake(ns_rec, mtcars %>% slice(1))
#> Error in if (num < 1) {: argument is of length zero

ns2_rec <- 
  recipe(mpg ~ ., data = mtcars) %>% 
  step_spline_natural(disp, deg_free = 3) %>% 
  prep()

bake(ns2_rec, mtcars %>% slice(1))
#> Error in if (num < 1) {: argument is of length zero

^{Created on 2023-08-25 with reprex v2.0.2}

For step_ns(), it is an issue with stripping off attributes (I assume the dim attribute).

For step_spline_natrual(), it is using I() rowwise that is dropping the dimension.

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