How to plot additional statistics in boxplot for each group?

Question

I would like to see boxplots of combination of factors and I was told to use lattice for that. I tried it and it looks like this:

enter image description here But now I would like to also add an ANOVA statistics to each of the groups. Possibly the statistics should display the p-value in each panel (in the white below the e.g. "Australia"). How to do this in lattice? Note that I don't insist on lattice at all...

Example code:

set.seed(123)
n <- 300
country <- sample(c("Europe", "Africa", "Asia", "Australia"), n, replace = TRUE)
type <- sample(c("city", "river", "village"), n, replace = TRUE)
month <- sample(c("may", "june", "july"), n, replace = TRUE)
x <- rnorm(n)
df <- data.frame(x, country, type, month)

bwplot(x ~ type|country+month, data = df, panel=function(...) {
    panel.abline(h=0, col="green")
    panel.bwplot(...)
})

The code to perform ANOVA for one of the groups and to extract p-value is this:

model <- aov(x ~ type, data = df[df$country == 'Africa' & df$month == 'may',])
p_value <- summary(model)[[1]][["Pr(>F)"]][2]

Arun · Accepted Answer · 2013-08-20 14:37:31Z

3

Here's one way using ggplot2. First we can compute the p-values separately for every month/country combination (I use data.table. you can use whichever way you're comfortable with). Then, we add geom_text and specify pvalue as the label and specify x and y coordinates where the text should be within each facet.

require(data.table)
dt <- data.table(df)
pval <- dt[, list(pvalue = paste0("pval = ", sprintf("%.3f", 
        summary(aov(x ~ type))[[1]][["Pr(>F)"]][1]))), 
        by=list(country, month)]

ggplot(data = df, aes(x=type, y=x)) + geom_boxplot() + 
geom_text(data = pval, aes(label=pvalue, x="river", y=2.5)) + 
facet_grid(country ~ month) + theme_bw() + 
theme(panel.margin=grid::unit(0,"lines"), # thanks to @DieterMenne
strip.background = element_rect(fill = NA), 
panel.grid.major = element_line(colour=NA), 
panel.grid.minor = element_line(colour=NA))

enter image description here

edited Aug 20, 2013 at 14:37

answered Aug 20, 2013 at 12:48

Arun

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10 Comments

Tomas Over a year ago

Thanks Arun! But please how to remove the awful ggplot grid? :) BTW very elegant use of datatables! Didn't know they are so elegant!

Tomas Over a year ago

better :) and if I want to get rid of it completely (so that it doesn't look like it is from ggplot :-))

Tomas Over a year ago

BTW the label placement by x="river", y=2.5 - isn't there something more flexible / independent of the actual coordinates?

Dieter Menne Over a year ago

# Avoid ugly ggplot shading: theme_set(theme_bw()+theme(panel.margin=grid::unit(0,"lines")))

Dieter Menne Over a year ago

You can use the them_set as written, but it also can be set globally to remove the ggplot-hyped-background overall.

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