在ggplot2上使用百分比刻度时如何设置间隔？

Question

I'm trying to manually enter when the breaks on the axis labels should be for my graph -- ie every 10 percentage points, every 25, etc, instead of having ggplot calculate them automatically.

ggplot(cars, aes(x=speed)) +
  geom_histogram(binwidth=.1, colour="white", fill="dark green", aes(y = (..count..)/sum(..count..))) + 
scale_x_continuous(labels=percent) +
scale_y_continuous(labels=percent) 

This is sort of random data, but shows the basic idea -- I would like to be able to set these in the:

scale_x_continuous(labels=percent)

in the same way as one can write that there should be breaks every x units using this code:

scale_x_continuous(breaks=seq(0,2, by=.1))

Does anyone have suggestions?

Answer 1

The breaks argument and the labels argument are not exclusive. The former is for determining where the breaks should be and the latter is for how they should be formatted/displayed. Thus you can do

scale_x_continuous(breaks = seq(0, 2, by = 0.1), labels = percent)

to specify both aspects.

Answer 2

Something like:

ggplot(cars, aes(x=speed)) +
  geom_histogram(binwidth=.1, colour="white", fill="dark green", aes(y = (..count..)/sum(..count..))) + 
  scale_x_continuous(breaks= seq(0,1,.1)*max(cars$speed), labels = seq(0,100,10)) + labs(x = "speed (%)")