Incremental graphs in ggplot2

[weiyangtham]

I am a fan of showing graphs layer by layer in slideshows. I find that my workflow ends up being something like

1. Make the final version of the graph that I want
2. Deconstruct the graph into the desired increments

This ends up involving a lot of copying and pasting. It's not the worst thing since ggplot syntax fits well with the layering idea, but I have found it to be enough work that I don't always do it. I've thought it would be nice to have some functions that can take a plot and show you just the parts you want. Roughly,

p = ggplot(mtcars, aes(mpg, wt)) + geom_point()
show_x_axis(p) # only shows x-axis
show_one_point(p) # only show one point so you can explain it

[maurolepore]

Sounds cool! Have you thought about how to implement it?
My first (and only idea) would be to edit the final call to the ggplot with the rlang package by @lionel- et al.

[wlandau]

Yeah, this sounds awesome! Such a natural consequence of ggplot2's layering paradigm.

In fact, ggplot2 objects already have a layers element.

library(ggplot2)
pl <- ggplot(mtcars) +
  geom_line(aes(x = wt, y = mpg)) +
  ggtitle("mpg vs wt") +
  geom_point(aes(x = wt, y = mpg, color = as.factor(cyl))) +
  ggtitle("mpg vs wt with line")

pl

pl$layers
#> [[1]]
#> mapping: x = ~wt, y = ~mpg 
#> geom_line: na.rm = FALSE
#> stat_identity: na.rm = FALSE
#> position_identity 
#> 
#> [[2]]
#> mapping: x = ~wt, y = ~mpg, colour = ~as.factor(cyl) 
#> geom_point: na.rm = FALSE
#> stat_identity: na.rm = FALSE
#> position_identity

# Remove a layer.
pl$layers <- pl$layers[-1]

pl

^{Created on 2019-03-07 by the reprex package (v0.2.1)}

But that's not what we want because both frames have "with line" in the title. Hence, @maurolepore's idea of computing on the language. A couple more ideas:

1. Walk the abstract syntax tree (AST), discover + signs, and make a new increment for each one.
2. Define increments manually, which would still require walking the AST to discover calls to increment().

pl <- ggplot(mtcars) +
  geom_line(aes(x = wt, y = mpg)) +
  ggtitle("mpg vs wt") +
  increment() +
  geom_point(aes(x = wt, y = mpg, color = as.factor(cyl))) +
  ggtitle("mpg vs wt with line") +
  increment()