How to convert long form data frame for contour plot

General Usage
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1

Hello,

As shown in the MWE below, I have a data frame with three variables in long form and would like to plot it as a contour plot. There are two issues. First, the variables x and y span a triangular area rather than a rectangular area. Second, the function contour requires x and y to be vectors and z to be a matrix. Unfortunately, contour does not handle data in long form.

What is the best way to handle these issues?

using DataFrames
using Plots 

df = DataFrame(x = Float64[], y = Float64[], z = Float64[])
vals = .01:.01:.99
for x ∈ vals, y ∈ vals
    if x + y ≤ 1 
        push!(df, [x y x * y])
    end
end
2

I usually use tricontourf in such cases: tricontourf | Makie. IMO it really is frustrating that it’s not possible to simply use contourf with flat vectors x \in \mathbb R^n, y \in \mathbb R^n and z \in \mathbb R^n, where z_i = f(x_i, y_i)\;\forall i.