How can i control bin intervals in ggplot2?

Question

I cant correctly control if a bin is going from e.g. -10 to +10 or from 0 to 20 when I say binwidth = 20 i get the former but I have data that begins at 1 and I dont want the interval to go into the negatives.

Here is an example of my problem:

testData = data.frame(x=c(1,4,6,9,9))

ggplot(data=testData, aes(x=testData$x)) +
  geom_histogram(binwidth=3, aes(col=I("white"))) +
  scale_x_continuous(breaks=c(1,2,3,4,5,6,7,8,9,10))

strange enough, if I use binwidth = 2 I end up with intervals like I want:

ggplot(data=testData, aes(x=testData$x)) +
  geom_histogram(binwidth=2, aes(col=I("white"))) +
  scale_x_continuous(breaks=c(1,2,3,4,5,6,7,8,9,10))

How can I get my bins to go from 1..20, 21..40, etc. for a larger dataset?

Answer 1

You can do this by using the argument center of geom_histogram as follows:

# Make some random test data
testData = data.frame(x=runif(1000,min=1,max=110))
# Construct the plot
ggplot(data=testData, aes(x=testData$x)) +
  geom_histogram(binwidth=20,
                 center = 11,
                 aes(col=I("white"))) +
  scale_x_continuous(breaks=seq(1,max(testData$x) + 20, by = 20))

By specifying the binwidth and the center for one bin, you define that the bin should be 20 wide and be centered around 11. So the first bin will be 1 to 21.

I also added a seq() call to construct the x axis ticks without having to type all of them manually. The resulting plot is the following: