r - 具有多个类的 hub_longer 会导致错误 ("No common type")

Question

我正在多列(即两个字符列和一个数字列)上运行 pivot_longer。我遇到与类不匹配相关的错误。

我已经调查了任何“强制”选项的文档，并且没有在pivot_longer中看到任何参数来指定要使用的类——或者允许函数自动检测最通用的类​​。

pivot_longer 中是否有任何参数可以避免此错误？或者您是否需要在运行 pivot_longer 之前将列转换为单个类？

library(dplyr)
library(tidyr)
library(ggplot2) # Just for `diamonds` dataset

small_diamonds <- diamonds %>% 
  # Select a few columns (two character, one numeric, specifically integers)
  select(cut, color, price) %>% 
  # Create a row_id
  mutate(row_num = row_number()) 

# This works with `gather`
small_diamonds %>% 
  gather(key, val, - row_num)

# This fails due to class error:
small_diamonds %>% 
  # Pivot data
  pivot_longer( - row_num, 
                names_to = "key",
                values_to = "val")

# Output
# Error: No common type for `cut` <ordered<4bd7e>> and `price` <integer>.
# Call `rlang::last_error()` to see a backtrace

# Convert columns to a single class (character) and then use `pivot_longer`. 
# Runs successfully
small_diamonds %>% 
  mutate_all(as.character) %>% 
  # Pivot data
  pivot_longer( - row_num, 
                names_to = "key",
                values_to = "val")

Answer 1

当使用 values_ptypes 参数时，错误现在以不同的形式再次出现。

library(tidyverse)

small_diamonds <- diamonds %>% 
  select(cut, color, price) %>% 
  mutate(row_num = row_number())

small_diamonds %>%  
  pivot_longer( - row_num, 
                names_to = "key",
                values_to = "val", 
                values_ptypes = list(val = 'character'))
#> Error: Can't convert <integer> to <character>.

因此我需要使用 values_transform 参数来获得所需的结果。

library(tidyverse)

  small_diamonds <- diamonds %>% 
    select(cut, color, price) %>% 
    mutate(row_num = row_number())
  
  small_diamonds %>%  
    pivot_longer( - row_num, 
                  names_to = "key",
                  values_to = "val", 
                  values_transform = list(val = as.character))
#> # A tibble: 161,820 x 3
#>    row_num key   val    
#>      <int> <chr> <chr>  
#>  1       1 cut   Ideal  
#>  2       1 color E      
#>  3       1 price 326    
#>  4       2 cut   Premium
#>  5       2 color E      
#>  6       2 price 326    
#>  7       3 cut   Good   
#>  8       3 color E      
#>  9       3 price 327    
#> 10       4 cut   Premium
#> # ... with 161,810 more rows

^{由reprex package于2020年8月25日创建(v0.3.0)}