R users adore the
ggplot2 package for all things data visualization. Its consistent syntax, useful defaults, and flexibility make it a fantastic tool for creating high-quality figures. Although
ggplot2 is great, there are other dataviz tools that deserve a place in a data scientist’s toolbox. Enter
plotly is a high-level interface to plotly.js, based on d3.js which provides an easy-to-use UI to generate slick D3 interactive graphics. These interactive graphs give the user the ability to zoom the plot in and out, hover over a point to get additional information, filter to groups of points, and much more. These interactive components contribute to an engaging user experience and allows information to be displayed in ways that are not possible with static figures.
The wonder of htmlwidgets
As you may have guessed, the “.js” in
There are two main approaches to initialize a
plotly object: transforming a
ggplot2 object with
ggplotly() or setting up aesthetics mappings with
ggplotly() takes existing
ggplot2 objects and converts them into interactive
plotly graphics. This makes it easy to create interactive figures while using the
ggplot2 syntax that we’re already used to. Additionally,
ggplotly() allows us to use
ggplot2 functionality that would not be as easily replicated with
plotly and tap into the wide range of
ggplot2 extension packages.
Let’s look at an example using the
mpg dataset from
library(dplyr) library(ggplot2) library(plotly) (ggplot_object <- mpg %>% ggplot(aes(x = displ, y = hwy)) + geom_point(mapping = aes(color = class)) + geom_smooth())
After saving a
ggplot2 object, the only step to
plotly-ize it is calling
ggplotly() on that object.
The difference between the two is that the
plotly figure is interactive. Try it out for yourself! Some of the interactive features to try out include hovering over a point to see the exact x and y values, zooming in by selecting (click+drag) a region, and subsetting to specific groups by clicking their names in the legend.
plot_ly() is the base
plotly command to initialize a plot from a dataframe, similar to
mpg %>% plot_ly(x = ~displ, y = ~hwy, color = ~class)
## No trace type specified: ## Based on info supplied, a 'scatter' trace seems appropriate. ## Read more about this trace type -> https://plot.ly/r/reference/#scatter
## No scatter mode specifed: ## Setting the mode to markers ## Read more about this attribute -> https://plot.ly/r/reference/#scatter-mode
Although we did not specify the plot type, it defaulted to a scatter plot. The type of plot is specified by setting the trace type. The
scatter trace type is the foundation for many low-level geometries (e.g., points, lines, and text), thus we must also specify a mode. To create a scatter plot with points the mode is set to
markers, but additional scatter modes include
plotly functions take a
plotly object as an input and return a modified
plotly object, making it work perfectly with the pipe (
mpg %>% plot_ly(x = ~displ, y = ~hwy, color = ~class) %>% add_trace(type = "scatter", mode = "markers")
Rather than using
add_trace() and specifying the type and mode, we can use the convenience function
mpg %>% plot_ly(x = ~displ, y = ~hwy, color = ~class) %>% add_markers()
Making other plot types is similarly easy by using the corresponding
add_*() function. See the documentation for a full list of traces: https://rdrr.io/cran/plotly/man/add_trace.html.
I was never taught about interactive graphics in school and never felt the need to learn it, but now I find uses for it all the time. Whether you are making a shiny app or just writing a statistical report I recommend trying out
plotly. There is not much of a learning curve due to the intuitive syntax, and it makes high quality graphics that are sure to impress. This post only scratches the surface of
plotly, but I hope this introduction gives you more confidence to try it out in your future work.