In ggplot2 how can I display in single legend the line color and point shape mapped to vector of single-character strings?

Haven't found any post that address this issue specifically.

In the following chart I'd like to use a column of single-character strings as the shapes for geom_point(). The help vignette ggplot2-specs says a single character string can be specified.

I want to see "4", "6", and "8" used as the point shapes (instead of circle, triangle, and square). But it doesn't seem to work. And if it did work, I'd like to see one legend (instead of two).

library(dplyr); library(ggplot2)

mtcars2 <- mtcars %>% 
  inner_join(data.frame(cyl=c(4,6,8), 
                        cyl_word=c('four','six','eight')))

p <- ggplot(mtcars2, aes(mpg, wt, color=cyl_word)) + geom_line()

p + geom_point(aes(shape=factor(cyl)), size=3)

Using geom_text() instead of geom_point() yields something closer to the desired results. What is missing from them is that the shapes ("4", "6", "8") don't appear in the legend (I suspect the letter "a" in the legend is the indicator of geom_text() and that it is unchangeable ... is that right?)

p + geom_text(aes(label=factor(cyl)), size=6)

Don't know if maybe I should be using scale_shape_?()

We can map the shape to cyl_word and force manual shapes:

ggplot(mtcars2, aes(mpg, wt, color=cyl_word)) +
  geom_line() +
  geom_point(aes(shape=cyl_word), size=3) +
  scale_shape_manual(values = setNames(as.character(mtcars2$cyl), mtcars2$cyl_word))

Clearly the order appears non-numeric, that can be address with factors.