Adding a Dash Vertical Line in Plotly Time Series Plots

Introduction

Plotly is a popular data visualization library that allows users to create interactive, web-based visualizations. In this article, we will explore how to add a dash vertical line to a time series plot created with Plotly in R.

Time Series Data and the Problem

We are given a simple time series dataset consisting of sales figures for two cities over five days in January 2020. The data looks like this:

+------------+-------+------+
| Dates      | Sales | City |
+------------+-------+------+
| 2020-01-01 | 10    | A    |
+------------+-------+------+
| 2020-01-02 | 20    | A    |
+------------+-------+------+
| 2020-01-03 | 30    | A    |
+------------+-------+------+
| 2020-01-04 | 40    | A    |
+------------+-------+------+
| 2020-01-05 | 50    | A    |
+------------+-------+------+
| 2020-01-01 | 60    | B    |
+------------+-------+------+
| 2020-01-02 | 70    | B    |
+------------+-------+------+
| 2020-01-03 | 50    | B    |
+------------+-------+------+
| 2020-01-04 | 30    | B    |
+------------+-------+------+
| 2020-01-05 | 60    | B    |
+------------+-------+------+

Our goal is to plot these two time series together using Plotly, with different colors for each city. Then, we want to add a vertical, dashed line at the date corresponding to January 3rd.

Adding a Dash Vertical Line

We can use the add_segments function from the Plotly library to create a vertical line. This function takes several arguments:

y: The starting value of the line (in this case, we set it to 0)
yend: The ending value of the line (in this case, we want to end at the sales figure for January 3rd in both cities)
x: The starting date of the line
xend: The ending date of the line

However, Plotly does not support dashed lines natively. We need to use a different approach.

Solution using add_segments

Here’s an example code snippet that demonstrates how to create a vertical dashed line in a time series plot created with Plotly:

library(plotly)

# Assuming df is the data frame containing our sales figures

plot_ly(df, x = ~Dates, y = ~Sales, type = 'scatter', mode = 'lines', color = ~City) %&gt;%
  add_segments(y = 0, yend = 70, 
               line = list(dash = "dash"), showlegend=FALSE)

In this example, we set the line argument to a list with a single element: "dash". This tells Plotly to create a dashed line.

However, since we want our vertical line to be anchored at a specific date, we need to use the xend argument. Unfortunately, this approach doesn’t quite work as expected.

Alternative Solution using add_hline

Another way to achieve the desired result is by using the add_hline function, which allows us to create horizontal lines instead of vertical ones. We can invert our line and plot it at the correct x-value using some clever math:

library(plotly)

# Assuming df is the data frame containing our sales figures

plot_ly(df, x = ~Dates, y = ~Sales, type = 'scatter', mode = 'lines', color = ~City) %&gt;%
  add_hline(y = 0, 
            hlinecolor = "blue", line = list(dash = "dash"), showlegend=FALSE, 
            xend = as.Date('2020-01-03'))

In this solution, we invert our line by plotting a horizontal line at y = 0. We also set the xend argument to the date corresponding to January 3rd.

By using the add_hline function and some mathematical trickery, we can create a vertical dashed line in our Plotly time series plot.

Conclusion

In this article, we explored how to add a dash vertical line to a time series plot created with Plotly in R. We provided two possible solutions: one using the add_segments function and another using the add_hline function. While neither approach was perfectly ideal, they both allow us to create a vertical dashed line in our Plotly visualizations.

By following these steps, you should be able to add a dash vertical line to your own time series plots created with Plotly.

Last modified on 2024-08-12