R plotly link subplots so that multiple tooltips shown on hover

Question

I have data with groups. For every group I plot a subplot in plotly. The x-values for all of these subplots correspond to identical description, just the y-axis value is either missing or different across groups. I would like to link these subplots so that if I hover over one point in one subplot, it will also highlight the points with the same x value in other subplots. I have tried the crosstalk package examples, but either I create the subplots wrong or I don't understand how to use it. Does anyone have any experience?

Update:

df <- data.frame(
     ID = rep(1:4, times = 2), 
     Value = rnorm(8),
     group = c(1,1,1,1,2,2,2,2)
 )

subplot(
     plot_ly(df[df$group==1,], x = ~ID, y = ~Value),
     plot_ly(df[df$group==2,], x = ~ID, y = ~Value), nrows = 2
 )

And my question is, how could I highlight the points with the same x value in all subplots if I hover on one of the points?

Answer 1

With the library crosstalk, you first need to transform your dataframe to a SharedData object to use in several connected plots.

With the function facet_grid(), you can create separate graphs according to the levels of a variable.

library(plotly)
library(crosstalk)
library(tidyverse)

df <- data.frame(
  ID    = rep(1:4, times = 2), 
  Value = rnorm(8), 
  group = c(1, 1, 1, 1, 2, 2, 2, 2)
)

shared_df <- SharedData$new(df)

ggplotly(
  shared_df %>%
    ggplot(aes(x = ID, y = Value)) + 
    geom_point() +
    facet_grid(~ group)
)

In the result, if you click on a point on the left graph, it will also highlight this same point on the right graph.