R - (ggplot) Make geom_step jumps dashed - r

Question

I'm plotting a discrete CDF. I have a few questions regarding geom_step which I'm not finding by using Google.
Is it possible to make the line segment representing the jump dashed
rather than solid to better show whats going on?
Is it possible to add geom_point more efficiently than I do? (less
c/p).
Below is my current solution:
library(tidyverse)
library(ggthemes)
theme_set(theme_few())
x0 <- seq(-0.5, -0.01, by = 0.01)
x1 <- seq(0, 0.99, by = 0.02)
x2 <- seq(1, 1.99, by = 0.02)
x3 <- seq(2, 2.99, by = 0.02)
x35 <- seq(3, 3.49, by = 0.01)
x4 <- seq(3.5, 3.99, by = 0.01)
tibble_ex <- tibble(
x0 = x0,
x1 = x1,
x2 = x2,
x3 = x3,
x35 = x35,
x4 = x4
)
tibble_ex %>%
gather(x, xax, x0:x4) %>%
mutate(cdf = case_when(x == 'x0' ~ 0,
x == 'x1' ~ 1/2,
x == 'x2' ~ 3/5,
x == 'x3' ~ 4/5,
x == 'x35' ~ 9/10,
x == 'x4' ~ 1)) %>%
ggplot(aes(x = xax, y = cdf)) +
geom_step() +
geom_point(aes(x = 0, y = 0), size = 3, shape = 21, fill = 'white') +
geom_point(aes(x = 1, y = 0.5), size = 3, shape = 21, fill = 'white') +
geom_point(aes(x = 2, y = 3/5), size = 3, shape = 21, fill = 'white') +
geom_point(aes(x = 3, y = 4/5), size = 3, shape = 21, fill = 'white') +
geom_point(aes(x = 3.5, y = 9/10), size = 3, shape = 21, fill = 'white') +
geom_point(aes(x = 0, y = 0.5), size = 3, shape = 21, fill = 'black') +
geom_point(aes(x = 1, y = 3/5), size = 3, shape = 21, fill = 'black') +
geom_point(aes(x = 2, y = 4/5), size = 3, shape = 21, fill = 'black') +
geom_point(aes(x = 3, y = 9/10), size = 3, shape = 21, fill = 'black') +
geom_point(aes(x = 3.5, y = 1), size = 3, shape = 21, fill = 'black') +
labs(x = 'x', y = 'F(x)')

Answer 1

ggplot will be more powerful to use if you can put your data into a data frame and structure it so that the characteristics of your data can be mapped directly.
Here's a way to take your data and augment it with additional rows that represent the connecting points, by matching each x with the prior cdf value. I added a column, type, to keep track of which is which. I also arrange df so that geom_segment plots the points in the right order.
new_steps <-
tibble(x = c(0:3, 3.5, 4),
cdf = c(0, .5, .6, .8, .9, 1))
df <- new_steps %>%
mutate(type = "cdf") %>%
bind_rows(new_steps %>%
mutate(type = "prior",
cdf = lag(cdf))) %>%
drop_na() %>%
arrange(x, desc(type))
Then we can map the points' fill and the geom_segments' linetype to type.
ggplot(df) +
geom_point(aes(x, cdf, fill = type),
shape = 21) +
scale_fill_manual(values = c("black", "white")) +
geom_segment(aes(x = lag(x), y = lag(cdf),
xend = x, yend = cdf,
lty = type)) +
scale_linetype_manual(values = c("dashed", "solid"))

Answer 2

(1) No, there is not a built-in way to make the geom_step half-dashed. But if you post this as a separate question, perhaps someone will help create a new geom for this.
(2) The answer is to put the points you want plotted in a data frame, like anything else you might want to plot:
point_data = data.frame(x = rep(c(0, 1, 2, 3, 3.5), 2),
y = c(0, rep(c(.5, .6, .8, .9), 2), 1),
z = rep(c("a", "b"), each = 5))
# calling your gathered/mutated version of tibble_ex df
ggplot(df, aes(x = xax, y = cdf)) +
geom_step() +
geom_point(data = point_data, aes(x = x, y = y, fill = z), shape = 21) +
scale_fill_manual(values = c("white", "black"), guide = FALSE) +
labs(x = 'x', y = 'F(x)')

Answer 3

For the second part of your question, you can put all the coordinates in a separate data frame and call geom_point only once:
ddf <- data.frame(xax = rep(c(0:3, 3.5), 2),
cdf = c(0, .5, .6, .8, .9, .5, .6, .8, .9, 1),
col = rep(c("white", "black"), each = 5))
dev.new()
tibble_ex %>%
gather(x, xax, x0:x4) %>%
mutate(cdf = case_when(x == 'x0' ~ 0,
x == 'x1' ~ 1/2,
x == 'x2' ~ 3/5,
x == 'x3' ~ 4/5,
x == 'x35' ~ 9/10,
x == 'x4' ~ 1)) %>%
ggplot(aes(x = xax, y = cdf)) +
geom_step() +
geom_point(data = ddf, aes(fill = I(col)), size = 3, shape = 21) +
labs(x = 'x', y = 'F(x)')