Horizontal/Vertical Line in plotly

Question

I'm using the plotly package and I'm trying to add a horizontal line to a graph. Is there any way of doing it using plotly?

It can be done using ggplot2 and the ggplotly function as shown below:

library(plotly)  p <- ggplot() +   geom_hline(yintercept = 4) +   xlim(c(0,10)) +   ylim(c(0,10))  ggplotly(p) 

But I can't add this to an existing plotly plot.

Also, the axis of my charts are not fixed, so it would be difficult (but not impossible) to just work out an x and y coordinate system for a horizontal line, but I'd rather just add one automatically.

I've looked into the y0 and dy arguments, but I can't seem to get the code for those to work, either. I'm not quite sure what they do exactly, but I think they're maybe what I'm looking for? I can't find good examples of their usage.

Answer 1

There are two main ways to do this (using either data or 'paper' coordinates). Assuming data coordinates, the easiest current way is via add_segments():

plot_ly() %>%   add_segments(x = 4, xend = 4, y = 0, yend = 10) %>%   add_segments(x = 3, xend = 5, y = 5, yend = 5) 

Notice how we've hard coded the extent of these lines in data coordinates; so when zooming and panning the plot, the line will be "clipped" at those values. If you don't want these lines to be clipped, use a line shape with xref/yref set to paper (this puts the graph region on a 0-1 scale, rather than on the x/y data scale):

vline <- function(x = 0, color = "red") {   list(     type = "line",      y0 = 0,      y1 = 1,      yref = "paper",     x0 = x,      x1 = x,      line = list(color = color)   ) }  hline <- function(y = 0, color = "blue") {   list(     type = "line",      x0 = 0,      x1 = 1,      xref = "paper",     y0 = y,      y1 = y,      line = list(color = color)   ) }  plot_ly() %>%   layout(shapes = list(vline(4), hline(5))) 

Answer 2

Alternatively, you could add a shape (i.e. line) under layout(). The following example adds a vertical line:

p <- plot_ly(data, x = ~x.data, y = ~y.data, text = ~text.data, type = 'scatter',         mode = 'markers', marker = list(size = ~size.data, opacity= 0.5)) %>%      layout(shapes=list(type='line', x0= 0.2, x1= 0.2, y0=min(allyvalues), y1=max(allyvalues), line=list(dash='dot', width=1)),        title = 'This is the Title',        xaxis = list(title = "X-Axis", showgrid = TRUE),        yaxis = list(title = "Y-Axis", showgrid = TRUE)) p