0

How do I plot a set of curves with Julia (1.4.1) and Plots in a Jupyter notebook, some of them using the x axis and the left y axis, and some (more than one!) using the x axis and the right y axis? Whatever I try, I always get only one plot (the first one, which gets the twinx command) to use the right y axis, whereas the ones following it use the first (left) axis again. Among several other things, I tried

epl=plot(title="A title",legend=:topright)
epl=plot!(x_arr,y1_arr)
epl=plot!(x_arr,y2_arr)
epl=plot!(twinx(),x_arr,y3_arr,legend=:bottomright)
epl=plot!(x_arr,y4_arr)
display((epl))

and also

epl=plot(title="A title",legend=:topright)
epl=plot!(x_arr,[y1_arr,y2_arr])
epl=plot!(twinx(),x_arr,[y3_arr,y4_arr],legend=:bottomright)
display((epl))

The latter works a bit better, but I don't know how to define individual linestyles, legend labels etc. for each vector element; my attempt to assign matching vectors to the corresponding keyword arguments failed. The label for the second y axis (not included in the example above) does not show up either. The legend is wrong in the first case and does not show up at all in the second case. The interface I use is apparently gr(), which I tend to prefer, but I'm not sure.

mbauman
  • 30,958
  • 4
  • 88
  • 123
TomR
  • 133
  • 1
  • 14

1 Answers1

2

The plot! function takes an optional first plot object to modify. If you don't pass in a plot to be modified, it uses the global one.

When you call twinx(), it creates a new subplot that you can plot! into — one that's inside your current global plot — and then it updates and returns the overall plot. Your next plot! just updates the first subplot as usual.

The key is to save your twinned subplot and explicitly plot! into it.

epl=plot(title="A title", legend=:topright)
plot!(x_arr, y1_arr) # could be explicitly `plot!(epl, x_arr, y1_arr)`
plot!(x_arr, y2_arr)
subplot = twinx()
plot!(subplot, x_arr, y3_arr, legend=:bottomright)
plot!(subplot, x_arr, y4_arr)
mbauman
  • 30,958
  • 4
  • 88
  • 123
  • That looks pretty good already! The only problem that remains right now is that the label of the right y axis still doesn't show up; I have specified it with the `ylabel` keyword in the first curve of the subplot. Actually, this even happens if I have only one curve for each axis. Is it possible that it is actually cut off, because the automatic sizing of the plot doesn't work correctly? – TomR Jan 08 '21 at 14:01