Plotly: Annotate outliers with sample names in boxplot

Question

I am trying to create a boxplot with ggplot and plotly with the dataset airquality where Month is on the x-axis and Ozone values are on y-axis. My aim is to annotate the plot so that when I hover over the outlier points it should show the Sample name in addition to the Ozone value:

library(tidyverse)
library(plotly)
library(datasets)
data(airquality)

# add months
airquality$Month <- factor(airquality$Month,
                           labels = c("May", "Jun", "Jul", "Aug", "Sep"))

# add sample names
airquality$Sample <- paste0('Sample_',seq(1:nrow(airquality)))

# boxplot
p <- ggplot(airquality, aes(x = Month, y = Ozone)) +
  geom_boxplot()
p <- plotly_build(p)
p

Here is the plot that's created:

By default, when I hover over each of the boxes, it shows the basic summary stats of the x-axis variable. However, what I would also like to see is what the outlier samples are. For e.g. when hovering over May, it shows the outlier value 115 but it does not show that it is actually Sample_30.

How can I add the Sample variable to the outlier points so it shows both the outlier value as well as the sample name?

Answer 1

We can almost get it like this:

library(ggplot2)
library(plotly)
library(datasets)
data(airquality)
# add months
airquality$Month <- factor(airquality$Month,
                           labels = c("May", "Jun", "Jul", "Aug", "Sep"))
# add sample names
airquality$Sample <- paste0('Sample_',seq(1:nrow(airquality)))
# boxplot
gg <- ggplot(airquality, aes(x = Month, y = Ozone)) +
  geom_boxplot()
ggly <- ggplotly(gg)
# add hover info
hoverinfo <- with(airquality, paste0("sample: ", Sample, "</br></br>", 
                                     "month: ", Month, "</br>",
                                     "ozone: ", Ozone))
ggly$x$data[[1]]$text <- hoverinfo
ggly$x$data[[1]]$hoverinfo <- c("text", "boxes")

ggly

Unfortunately, the hovering does not work for the first box plot...