Confusing error message when no optimization package is loaded

[salbalkus]

Consider the following code snippet:

using DensityRatioEstimation
x = randn(100)
y = randn(100) .+ 1
DensityRatioEstimation.fit(KLIEP, x, y, LCV((σ=1,b=50)))

This throws MethodError: no method matching iterate(::Nothing). The actual issue here, it appears, is that the necessary optimization package is not loaded; adding using Optim at the start fixes the problem. However, the error that is thrown obviously does not describe this problem accurately, making the problem difficult to debug for users unfamiliar with how DensityRatioEstimation.jl works.

Perhaps it would be convenient to throw a more descriptive error when this occurs. I have found this package super useful and I think this could be a good quality-of-life addition.

[juliohm]

Thank you for reporting the issue @salbalkus. Would you like to submit a PR that adds a more descriptive error message? The current error message is "not implemented", and you can find it here:

DensityRatioEstimation.jl/src/kliep.jl

Line 63 in 4ffd7a4

_kliep_coeffs(K_nu, K_de, dre::KLIEP, optlib::Type{<:OptimizationLibrary}) = @error "not implemented"

A more descriptive message would include a note to the different optimization libs available for KLIEP, which must be loaded to trigger implementations.

[juliohm]

@salbalkus need some help to prepare a pull request?

https://github.com/firstcontributions/first-contributions

[salbalkus]

@salbalkus need some help to prepare a pull request?

https://github.com/firstcontributions/first-contributions

Hi Júlio, thank you for the response and helpful link! I am preoccupied today but I can prepare a pull request next week 👍

[juliohm]

Fixed on master. Thanks!