gradient breaks in a ggplot stat_bin2d plot

Question

I have a 2d histogram created with stat_bin2d in the ggplot2 package. I'd like to control both the number of breaks in the color gradient, as well as where those breaks are located. I'm sure I'm just overlooking something small, but I can't figure out how to control the breaks in the binning.

Example:

x <- rnorm(100)^2
y <- rnorm(100)^2
df <- data.frame(x,y)
require(ggplot2)
p <- ggplot(df, aes(x, y)) 
p <- p + stat_bin2d(bins = 20)
p + scale_colour_gradient2(breaks=c(1,2,3,4,5,6))

This produces:

This plot only has 3 breaks at c(5,10,15) despite my futile attempt to put breaks at c(1,2,3,4,5,6))

Any hints?

Mazonson

Your plot makes me want to play Atari. – Grannia

Have a look at #50507332 – Paratyphoid

Answer 1

here is an example combining cut and bin2d:

p <- ggplot(df, aes(x, y, fill=cut(..count.., c(0,6,8,9,Inf))))
p <- p + stat_bin2d(bins = 20)
p + scale_fill_hue("count")

As there are many ways to make the breaks arbitrary, if you define clearly what you want, probably you can get a better answer.

Oppen

I can't get a better answer than this. It's exactly what I was looking for. Thanks! – Mazonson

I like the solution, but I wonder if there is a way to get the scale to be marked at the (0, 6, 8, 9, Inf) breakpoints rather than denote them by ranges. – Amontillado

Answer 2

Me thinks you probably want the less talked about cousin of scale_colour_gradient2(), scale_fill_gradient2()

Using your data:

p + scale_fill_gradient2(breaks=c(1,2,3,4,5,6))

Also note the optional parameters low, mid, and high for additional controls.

Balakirev

The colours in the legend do not match those used on the plot. – Managing

@Gavin - hmm, good catch. It looks like the entire range of values is being plotted, and breaks are only shown where specified...a bit strange. I wonder if that's the intended action? Regardless, adding limits = c(1,6) seems to give more intuitive values for the legend to match what is actually plotted. There may be other alternatives as well, so this isn't meant to be exhaustive. – Balakirev

@Gavin @Balakirev - Setting limits = c(1,6) makes the legend colors match the plots (for me at least) but I confess I don't have an explanation. – Inspan

Breaks are like axis tick marks. Changing them just changes the legend, it doesn't modify the scale in any way. – Bevon

Also I doubt you really want gradient2 give that there's no natural midpoint. – Bevon

Hadley, is there a way to change the scale? – Mazonson

@JDLong What part of scale do you want to change? If you tell a desired output, maybe I can tell something. – Oppen

@kohske, I just want to make the breaks arbitrary. This example is, of course, just a simple illustration of the problem. An example would be to make 4 buckets: 1-6, 6-8, 8, >9. – Mazonson

@JD - you could always define your buckets previously with cut and then pass that as the aesthetic. – Balakirev

@chase, possibly because I don't use ggplot very much, but I don't know how to define the buckets with cut and pass that as an aesthetic. Sounds like the basis of a good answer thought! – Mazonson

@JD - looks like kohske picked up on my random musings and offered a pretty slick solution. I think he's leading you on the path to ggplot righteousness. – Balakirev