使用ggplot2同时按颜色和线型分组绘图触发报错的问题

1. 从CSV列构建DataFrame，检查后数据无异常：

position <- (SCATGRAPH$position)
species <- (SCATGRAPH$species)
value <- (SCATGRAPH$value)
habitat <- (SCATGRAPH$habitat)
df <- data.frame(position,species,value,habitat)

2. 尝试绘制包含4条线的折线图，通过颜色区分species、线型区分position，代码如下：

ggplot(data=df, aes(x=habitat, y=value, group=species, colour=species, linetype=position)) + geom_line() + geom_point()

运行代码后未生成图表，触发报错：

Error in geom_line():
! Problem while converting geom to grob.
ℹ Error occurred in the 1st layer.
Caused by error in draw_panel():
! geom_line() can't have varying colour, linewidth, and/or
alpha along the line when linetype isn't solid
Run rlang::last_error() to see where the error occurred.

执行rlang::last_error()得到回溯信息：

Backtrace:
  1. base (local) `<fn>`(x)
  2. ggplot2:::print.ggplot(x)
  4. ggplot2:::ggplot_gtable.ggplot_built(data)
  5. ggplot2:::by_layer(...)
 12. ggplot2 (local) f(l = layers[[i]], d = data[[i]])
 13. l$draw_geom(d, layout)
 14. ggplot2 (local) draw_geom(..., self = self)
 15. self$geom$draw_layer(...)
 16. ggplot2 (local) draw_layer(..., self = self)
 17. base::lapply(...)
 18. ggplot2 (local) FUN(X[[i]], ...)
 20. self$draw_panel(data, panel_params, coord, na.rm = FALSE)
 21. ggplot2 (local) draw_panel(..., self = self)

3. 仅按单一因子（颜色或线型）分组时，代码可正常运行，示例：

ggplot(data=df, aes(x=habitat, y=value, group=species, colour=species))+ geom_line() 

将colour替换为linetype，或把species替换为position，对应代码也能正常执行。

4. 已尝试多种解决方案：单独在geom_line中设置aes(linetype=position)、调整语法结构、添加scale_linetype_manual命令、将species或position转为因子，均无法解决报错问题。

补充数据集：

structure(list(habitat = structure(c(1L, 1L, 2L, 2L, 3L, 3L, 
4L, 4L, 1L, 1L, 2L, 2L, 3L, 3L, 4L, 4L), levels = c("Upland interior", 
"Upland edge", "Peatland edge", "Peatland interior"), class = "factor"), 
    position = structure(c(2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 
    1L, 2L, 1L, 2L, 1L, 2L, 1L), levels = c("On", "Off"), class = "factor"), 
    species = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 
    2L, 2L, 2L, 2L, 2L, 2L, 2L), levels = c("Deer", "Moose"), class = "factor"), 
    value = c(0.428571429, 0.31372549, 0.315789474, 0.315789474, 
    0.263157895, 0, 0.166666667, 0, 0.285714286, 0.196078431, 
    0, 0.263157895, 0.052631579, 0.157894737, 0, 0.15)), row.names = c(NA, 
-16L), class = "data.frame")

内容的提问来源于stack exchange，提问作者Joel Plaskett