Missing datapoints when using hvplot,line

HoloViews
1

I am rendering a time series using hvplot.line. When zooming in on the plot, I noticed some of the lines were disappearing where there should be data points. The lines are disappearing as the zoom increases. How can I control or avoid that?

This behavior is more clear when overlaying line- and scatter-plots of the same dataset.
The following code should reproduce the issue:

import xarray as xr
import holoviews as hv
import hvplot.xarray

url = "https://thredds.met.no/thredds/dodsC/alertness/YOPP_supersite/obs/utqiagvik/utqiagvik_obs_timeSeries_20180701_20180930.nc"
ds = xr.open_dataset(url)

# the following line plot which has data disappearing as we zoom in
ds['snd'].hvplot.line(x='time01')

# overlay showing missing data points in the line plot:
hv.Overlay([ds['snd'].hvplot.line(x='time01'), 
            ds['snd'].hvplot.scatter(x='time01')]).opts(show_grid=True)
2

I have a hard time recreating this is it possible to make a screen recording?

3

I tried to record an example here: No title available. Video i...

It seems the issue is related to the Y limit on the plot - when I fine tune the Y zoom to let the data “fit” in the plot canvas, then all the points are connected and the line plot is representative of the dataset - otherwise, the line plot is removing lines where actual data exist.

4

By looking at it, this is because it is only a single value surrounded by nan values. A line needs two points to be shown.

Can you check the data if this is the case?

5

Yes, that is exactly it! Thank you so much for clarifying the behavior. It is intuitive and visible when there is a large gap large data - gap in the data, but It is somehow confusing to see lines disappearing when zooming in. If I understood, this means that the line is shown because there is a sort of downsampling when zoomed out? why if I “adjust” the y-lim in the plot the NaN is ignored and a line is plotted?

6

There is no downsampling happening; what is happening at the end of your video should not happen.

What versions of Bokeh and HoloViews are you using? Can you try hv.renderer('bokeh').webgl = False and see if this changes the behavior?

7

Using hv.renderer('bokeh').webgl = False - I no longer see lines disappearing!

8

I think this should be fixed on the latest version of Bokeh.

9

Wonderful! Thank you so much for your help.
I am running:

Python 3.11.6 | packaged by conda-forge | (main, Oct  3 2023, 10:40:35) [GCC 12.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import bokeh
>>> bokeh.__version__
'3.3.3'

I will try to install the 3.4.0.dev5 version and see if that fixes it.

1 Like