Continuous color causes error when x or y is factor

When I try to take color from numeric variable and one of the axes is factor, it raises error Error in Summary.factor(...) : ‘range’ not meaningful for factors:

data(mpg)
mpg$classF <- as.factor(mpg$class)

# error when x is factor AND color is numeric:
mpg %>% 
  plot_ly(x = ~classF, y = ~cyl, color = ~displ) %>%
  add_markers()
# Error in Summary.factor(c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,  : 
#                             ‘range’ not meaningful for factors

# works fine when x is character:
mpg %>% 
  plot_ly(x = ~class, y = ~cyl, color = ~displ) %>%
  add_markers()

# also works fine if color is factor or character:
mpg %>% 
  plot_ly(x = ~classF, y = ~cyl, color = ~as.character(displ)) %>%
  add_markers()

首先，在 R 会话中运行提供的 mpg 示例，以复现 factor-axis 和 numeric-color 的失败。跟踪对 factor 数据调用 range 的颜色处理；当失败的示例能够无错误运行，同时 character-axis 和 factor-or-character-color 情况仍能正常工作时，即表示完成。