contor with no points: draw nothing instead of throwing an error

[tecosaur]

Heyo,

So, as mentioned in #2077 I have some data that starts off with no points (and can drop down to 0-1 points) that I want to draw contour lines from.

Unfortunately, this isn't as easy as calling contour! on the data observers.

With zero points, you see this error:

julia> contour([], [], [])
ERROR: `Makie.convert_arguments` for the plot type Combined{Makie.contour, Tuple{Vector{Any}, Vector{Any}, Vector{Any}}} and its conversion trait ContinuousSurface() was unsuccessful.

The signature that could not be converted was:
::Vector{Any}, ::Vector{Any}, ::Vector{Any}

With one point, you see this error:

julia> contour([1], [1], [1])
ERROR: Can't interpolate in a range where cmin == cmax. This can happen, for example, if a colorrange is set automatically but there's only one unique value present.

I feel like it would be rather reasonable with 0-1 points to just not draw anything.

[SimonDanisch]

Have you actually tried the suggestion from the error message as a work around?

contour([1], [1], [1]; colorrange=(0, 1))

Seems to work fine and also allows updating the plot.

[tecosaur]

Have you actually tried the suggestion from the error message as a work around?

I have, but that only helps in the 1-point case, and so doesn't actually help me at all.

[tecosaur]

Also, even if that did fix it, it would feel like a cludge as I'd have to turn that into an observable to change the colour range based on the data with a 1-point special case.

[SimonDanisch]

Well, 10x better then deleting the plot object ;)

I have, but that only helps in the 1-point case, and so doesn't actually help me at all.

Can you supply an example? This has 0 points and works:

f, ax, pl = contour(zeros(5, 5); colorrange=(0, 1))

[tecosaur]

Isn't that a set of 0-valued points, not 0 points? I mean this:

contour([], [], []; colorrange=(0, 1))

[SimonDanisch]

Ah, sorry... When you said points, I was thinking of the line points, and not some input matrix/vector... Yeah ok that still doesn't work.

[jkrumbiegel]

contour([], [], []; colorrange=(0, 1))

Well for one I think you need to type those vectors because there are no conversion methods for Any vectors