`recipes::step_num2factor()` - tidymodels出错

Question

在定义了一个recipe()之后，使用tidymodels方法调用recipes::prep()时，我得到一个错误。在食谱定义过程中，我似乎误用了recipes::step_num2factor()，但我不明白哪里出了问题。

加载包

library(tidyverse)  # data wrangling
library(tidymodels)  # modelling

提供数据

data <- 
  tibble::tribble(
  ~Survived, ~Pclass,
         1L,      1L,
         1L,      2L,
         0L,      3L
  )

定义食谱

titanic_recipe <- 
  
  # define model formula:
  recipe(Survived ~ Pclass, data = data) %>%
  
  # convert numeric outcome to nominal (factor):
  step_num2factor(Survived,
                  levels = c("dead", "alive"))   

准备食谱

prep(titanic_recipe)  # THROWS ERROR

上面的live抛出了这个错误：

Error: Assigned data `map_df(...)` must be compatible with existing data.
x Existing data has 3 rows.
x Assigned data has 2 rows.
ℹ Only vectors of size 1 are recycled.

我不明白为什么会出现这个错误。

Answer 1

因子级别不能为0，它们应从1开始。因此，您可以向step()函数添加transform参数以添加1。以下修改效果良好

titanic_recipe <- 
  recipe(Survived ~ Pclass, data = data) %>%
  step_num2factor(Survived,
                  levels = c("dead", "alive"),
                  transform = function(x) x+1)   
titanic_recipe

prep(titanic_recipe) %>% juice()

# A tibble: 3 x 2
  Pclass Survived
   <int> <fct>   
1      1 alive   
2      2 alive   
3      3 dead