ggerrorbard

Building on ggplot2, the goal of ggerrorbard is to draw diagonal error bars (instead of standard vertical or horizontal error bars).

Installation

You can install the development version of ggerrorbard from GitHub like this:

# install.packages("devtools")
devtools::install_github("lmwidmayer/ggerrorbard")

Example

This is a basic example how to plot the error bars:

library(ggplot2)
library(ggerrorbard)

set.seed(12)

# dummy data
dat <- data.frame(x = c(rnorm(10, m = 1, sd = 1), 
                        rnorm(10, m = 4, sd = 2)), 
                  y = c(rnorm(10, m = 1, sd = 1.5),
                        rnorm(10, m = 3, sd = 1.8)),
                  session = c(rep(letters[1:2], each = 10)))
dat$d <- with(dat, y - x)

# summary of data
m <- aggregate(cbind(x, y) ~ session, 
               data = dat, 
               mean)
m$sd <- aggregate(d ~ session, 
                  data = dat, 
                  sd)[, 2] / sqrt(aggregate(d ~ session, 
                                            data = dat, 
                                            length)[, 2])
m$n <- aggregate(d ~ session, 
                                            data = dat, 
                                            length)[, 2]
m$se <- m$sd / sqrt(m$n)

# plot
ggplot(data = dat,
       mapping = aes(x = x, y = y,
                     group = session,
                     color = session)) +
  geom_abline(intercept = 0, slope = 1) +
  geom_point(alpha = 0.4, size = 2) +
  geom_point(data = m,
             mapping = aes(x = x, y = y,
                           group = session,
                           color = session),
             size = 4) +
  ggerrorbard::geom_errorbard(data = m,
                 mapping = aes(xcenter = x, ycenter = y, # center points of error bars
                               group = session,
                               color = session,
                               latitude = 2*se, # width of error bars
                               angle = -45), # angle of error bars
                 # arrows on ends of error bars
                 arrow = arrow(angle = 90, 
                               ends = "both", 
                               length = unit(0.05, "npc")),
                 linewidth = 1.1) +
  ggtitle("Pairwise difference") +
  coord_equal() +
  theme_minimal()

Limitations

• The error bars get distorted by transformations of the plotting coordinate system, e.g. coord(x = "log10", y = "log10")