Allow features to be `AbstractVector` (in addition to `AbstractMatrix`)

[sanderbboisen]

I was playing around with DecisionTree.jl for a potential project and found that I could not produce a regression tree from a single feature. I have made changes to allow features to be a vector in the build_tree functions.

I have tested the changes using RunTest.jl with Julia 1.6.4 .

[ablaom]

I don't see any harm in this enhancement, apart from a mild complication in the codebase.

Anyone else have objections?

@sanderbboisen Would you be willing to add a test of native and ScikitLearn API with a vector X ?

[sanderbboisen]

I don't see any harm in this enhancement, apart from a mild complication in the codebase.

Anyone else have objections?

@sanderbboisen Would you be willing to add a test of native and ScikitLearn API with a vector X ?

Sure, I will get on it. Incoming update.

[codecov-commenter]

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[sanderbboisen]

I ran into an issue as several functions like apply_something were overloaded so that any Vector inputs worked differently. These are essentially only called by theapply_something functions that users are supposed to call. I have taken the path of least modification, and named them _apply_something. This way users only have access to the functions they are intended to use, and using Vectors as inputs work.

I have added tests to tests/scikitlearn.jl and everything seems to work.

I am sorry for the confusing commit structure, things got a little messy at some point.

I think there is a general issue with the way that the module is constructed, and I have been refactoring it in a separate branch on my fork. For one, the structure does not allow multiple usage of utils.jl and there is generally some issues with code repetition iirc. I will open another PR on this when I am done refactoring.

[ablaom]

I am happy with this now.

I suspect this smaller PR may create a few merge conflicts for the more complicated #166, so let's wait for:

• [x] #166 is merged

before merging this one.

@sanderbboisen Thanks for your contribution and patience.

[ablaom]

@sanderbboisen Would you now be happy to rebase your PR?