Pete900 Pete900 - 3 months ago 41
R Question

Change axis breaks without defining sequence - ggplot

Is there any way to set the break step size in ggplot without defining a sequence. For example:

x <- 1:10
y <- 1:10

df <- data.frame(x, y)

# Plot with auto scale
ggplot(df, aes(x,y)) + geom_point()

# Plot with breaks defined by sequence
ggplot(df, aes(x,y)) + geom_point() +
scale_y_continuous(breaks = seq(0,10,1))

# Plot with automatic sequence for breaks
ggplot(df, aes(x,y)) + geom_point() +
scale_y_continuous(breaks = seq(min(df$y),max(df$y),1))

# Does this exist?
ggplot(df, aes(x,y)) + geom_point() +
scale_y_continuous(break_step = 1)


You may say I am being lazy but there have been a few occasions where I have had to change the
min
and
max
limits of my
seq
due to the addition of error bars. So I just want to say...use a break size of x, with automatic scale limits.

Answer

You can define your own function to pass to the breaks argument. An example that would work in your case would be

f <- function(y) seq(floor(min(y)), ceiling(max(y)))

Then

ggplot(df, aes(x,y)) + geom_point() + scale_y_continuous(breaks = f)

gives

enter image description here

You could modify this to pass the step of the breaks, e.g.

f <- function(k) {
        step <- k
        function(y) seq(floor(min(y)), ceiling(max(y)), by = step)       
}

then

ggplot(df, aes(x,y)) + geom_point() + scale_y_continuous(breaks = f(2))

would create a y-axis with ticks at 2, 4, .., 10, etc.

You can take this even further by writing your own scale function

my_scale <- function(step = 1, ...) scale_y_continuous(breaks = f(step), ...)

and just call it like

ggplot(df, aes(x,y)) + geom_point() + my_scale()

I think that shouldn't break anything, but you can never be sure :)