how to distinguish 4 factors in ggplot2? - r

Question

How does one distinguish 4 different factors (not using size)? Is it possible to use hollow and solid points to distinguish a variable in ggplot2?
test=data.frame(x=runif(12,0,1),
y=runif(12,0,1),
siteloc=as.factor(c('a','b','a','b','a','b','a','b','a','b','a','b')),
modeltype=as.factor(c('q','r','s','q','r','s','q','r','s','q','r','s')),
mth=c('Mar','Apr','May','Mar','Apr','May','Mar','Apr','May','Mar','Apr','May'),
yr=c(2010,2011,2010,2011,2010,2011,2010,2011,2010,2011,2010,2011))
where x are observations and y are modeling results and I want to compare different model versions across several factors. Thanks!

Answer 1

I think , it very difficult visually to distinguish/compare x and y values according to 4 factors. I would use faceting and I reduce the number of factors using interaction for example.
Here an example using geom_bar:
set.seed(10)
library(reshape2)
test.m <- melt(test,measure.vars=c('x','y'))
ggplot(test.m)+
geom_bar(aes(x=interaction(yr,mth),y=value,
fill=variable),stat='identity',position='dodge')+
facet_grid(modeltype~siteloc)

Answer 2

I really like using interaction by agstudy - I would probably try this first. But if keeping things unchanged then:
4 factors could be accomodated with faceting and 2 axes. Then there are 2 metrics x and y: one option is a bubble chart with both metrics distinguishing by color or shape or both (added jitter to make shapes less overlapping):
testm = melt(test, id=c('siteloc', 'modeltype', 'mth', 'yr'))
# by color
ggplot(testm, aes(x=siteloc, y=modeltype, size=value, colour=variable)) +
geom_point(shape=21, position="jitter") +
facet_grid(mth~yr) +
scale_size_area(max_size=40) +
scale_shape(solid=FALSE) +
theme_bw()
#by shape
testm$shape = as.factor(with(testm, ifelse(variable=='x', 21, 25)))
ggplot(testm, aes(x=siteloc, y=modeltype, size=value, shape=shape)) +
geom_point(position="jitter") +
facet_grid(mth~yr) +
scale_size_area(max_size=40) +
scale_shape(solid=FALSE) +
theme_bw()
# by shape and color
ggplot(testm, aes(x=siteloc, y=modeltype, size=value, colour=variable, shape=shape)) +
geom_point(position="jitter") +
facet_grid(mth~yr) +
scale_size_area(max_size=40) +
scale_shape(solid=FALSE) +
theme_bw()
UPDATE:
This is attempt based on 1st comment by Dominik to show if (x,y) is above or below 1:1 line and how big is the ratio x/y or y/x - blue triangle is if x/y>1, red circle otherwise (no need in melt in this case):
test$shape = as.factor(with(test, ifelse(x/y>1, 25, 21)))
test$ratio = with(test, ifelse(x/y>1, x/y, y/x))
ggplot(test, aes(x=siteloc, y=modeltype, size=ratio, colour=shape, shape=shape)) +
geom_point() +
facet_grid(mth~yr) +
scale_size_area(max_size=40) +
scale_shape(solid=FALSE) +
theme_bw()

Answer 3

You can use hollow and solid points, but only with certain shapes as described in this answer.
So, that leaves you with fill, colour, shape, and alpha as your aesthetic mappings. It looks ugly, but here it is:
ggplot(test, aes(x, y,
fill=modeltype,
shape=siteloc,
colour=mth,
alpha=factor(yr)
)) +
geom_point(size = 4) +
scale_shape_manual(values=21:25) +
scale_alpha_manual(values=c(0.35,1))
Ugly, but I guess it is what you asked for. (I haven't bothered to figure out what is happening with the legend -- it obviously isn't displaying the borders right.)
If you want to map a variable to a kind of custom aesthetic (hollow and solid), you'll have to go a little further:
test$fill.type<-ifelse(test$yr==2010,'other',as.character(test$mth))
cols<-c('red','green','blue')
ggplot(test, aes(x, y,
shape=modeltype,
alpha=siteloc,
colour=mth,
fill=fill.type
)) +
geom_point(size = 10) +
scale_shape_manual(values=21:25) +
scale_alpha_manual(values=c(1,0.5)) +
scale_colour_manual(values=cols) +
scale_fill_manual(values=c(cols,NA))
Still ugly, but it works. I don't know a cleaner way of mapping both the yr to one colour if it is 2010 and the mth if not; I'd be happy if someone showed me a cleaner way to do that. And now the guides (legend) is totally wrong, but you can fix that manually.