41

Is there a way to plot an infinite horizontal line with Bokeh? The endpoints of the line should never become visible, no matter how far out the user is zooming.

This is what I've tried so far. It just prints an empty canvas:

import bokeh.plotting as bk
import numpy as np

p = bk.figure()
p.line([-np.inf,np.inf], [0,0], legend="y(x) = 0")
bk.show(p)

One way would be to set the endpoints extremely high/low and the figure's x_range and y_range very small in relation to them. 

import bokeh.plotting as bk
import numpy as np

p = bk.figure(x_range=[-10,10])
p.line([-np.iinfo(np.int64).max, np.iinfo(np.int64).max], [0,0], legend="y(x) = 0")
bk.show(p)

However, I am hoping that somebody has a more elegant solution.

Edit: removed outdated solution

Tobias Hotzenplotz
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    If you're using the line to emphasize different plot regions, you may be interested in the new [BoxAnnotations](http://bokeh.pydata.org/en/latest/docs/user_guide/plotting.html#box-annotations)! – Eike P. Oct 02 '15 at 12:09
  • Please consider changing the accepted answer, either `Span` or `BoxAnnotation` are better than the old accepted answer. – bigreddot Jan 26 '16 at 17:48
  • You are right. Both solutions work great. I chose the spans because I think they are more "meant to be used" for what I intended than infinite rays, if that makes any sense. – Tobias Hotzenplotz Jan 27 '16 at 23:06

4 Answers4

62

You are looking for "spans":

Spans (line-type annotations) have a single dimension (width or height) and extend to the edge of the plot area.

Please, take a look at http://docs.bokeh.org/en/latest/docs/user_guide/basic/annotations.html#spans

So, the code will look like:

import numpy as np
import bokeh.plotting as bk
from bokeh.models import Span

p = bk.figure()

# Vertical line
vline = Span(location=0, dimension='height', line_color='red', line_width=3)
# Horizontal line
hline = Span(location=0, dimension='width', line_color='green', line_width=3)

p.renderers.extend([vline, hline])
bk.show(p)

With this solution users are allowed to pan and zoom at will. The end of the lines will never show up.

Tarick Welling
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Daniel Perez-Gil
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    I am wondering: lines, circles and other glyphs can be drawn based on a "source". We can feed a ColumnDataSource into this. This enables us to change the ColumnDataSource and thus create interactive plots with a Bokeh server. My question: Do annotations like Span work in the same way? In other words, can I move the vertical line around as well by linking up the value of "location" to a slider? – Thornhale Jul 06 '17 at 00:03
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    This question is answered in this [post](https://stackoverflow.com/questions/76122690/updating-the-location-of-a-horizontal-line-based-on-a-slider-value-in-bokeh/76127040#76127040). – mosc9575 Apr 28 '23 at 07:07
11

The Bokeh documentation on segments and rays indicates the following solution (using ray):

To have an “infinite” ray, that always extends to the edge of the plot, specify 0 for the length.

And indeed, the following code produces an infinite, horizontal line:

import numpy as np
import bokeh.plotting as bk
p = bk.figure()
p.ray(x=[0], y=[0], length=0, angle=0, line_width=1)
p.ray(x=[0], y=[0], length=0, angle=np.pi, line_width=1)
bk.show(p)
bigreddot
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Eike P.
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6

If you plot two rays from the middle they won't get smaller as you zoom in or out since the length is in pixel. So something like this:

p.ray(x=[0],y=[0],length=300, angle=0, legend="y(x) = 0")
p.ray(x=[0],y=[0],length=300, angle=np.pi, legend="y(x) = 0")

But if the user pans in either direction the end of the ray will show up. If you can prevent the user from panning at all (even when they zoom) then this is a little nicer code for a horizontal line.

If the user is able to zoom and pan anywhere they please, there is no good way (as far as I can tell) to get a horizontal line as you describe.

Alejandro
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1

In case you are wondering how to use spans in combination with time series, convert your dates to unix timestamps:

start_date = time.mktime(datetime.date(2018, 3, 19).timetuple())*1000
vline = Span(location=start_date,dimension='height', line_color='red',line_width=3)

Or see this link for a full example.

bigreddot
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Guido
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