Increase the default number of breaks for ggplot scale

Question

I like to make a ggplot theme where the default number of axis breaks is double the default. I'm not sure what setting to update. I can see from this question that ggplot calculates the breaks using labeling::extended. From the doc I can see that the argument m controls the number of breaks:

Usage
extended(dmin, dmax, m, Q = c(1, 5, 2, 2.5, 4, 3), only.loose = FALSE, w = c(0.25, 0.2, 0.5, 0.05))

m number of axis labels

This gets passed from scales::extended_breaks which I can see has the default set to 5:

 function (n = 5, ...) 
    {
        n_default <- n
        function(x, n = n_default) {
            x <- x[is.finite(x)]
            if (length(x) == 0) {
                return(numeric())
            }
            rng <- range(x)
            labeling::extended(rng[1], rng[2], n, ...)
        }
    }

So is there a theme setting I could change to default n to e.g. 10?

theme_more_ticks <- function(nticks = 10) {
    theme_minimal() +
    ...?
}

I know that breaks for an individual plot can be changed in many ways (ref). However, I would like all plots I produce with this theme to have double the number of breaks they would have with the default theme.

Maybe I'm missing the point, but why not use the breaks argument in the appropriate scale_xxx_yyy function? — Limey
I want to change the default setting instead of adding scale_xxx_yyy to every plot. — Pete900

Limey Limey · Accepted Answer · 2020-07-17T10:30:45

My apologies. I overlooked the word "theme" in the first line of your post.

I don't think you can do what you want using themes, because as I understand it, themes affect the appearance of ggplot2 elements, not the algorithms used to calculate their number, position, values etc. The best I could do was to modify the functions used to construct the ggplot object. For example

mtcars %>% ggplot() + geom_point(aes(x=cyl, y=mpg))

gives

But

scale_x_continuous <- function(...) ggplot2::scale_x_continuous(..., breaks=scales::extended_breaks(n=10, ...))
mtcars %>% ggplot() + geom_point(aes(x=cyl, y=mpg))

produces

So rather than redefining the theme, overwrite the various scale_xxxx_yyyy functions. That's a similar one-off task to redefining the default theme.

Check my handling of .... I've not checked it and I've got it wrong in the past.

Does that help?

Increase the default number of breaks for ggplot scale

1 Answers