Overload Compat.eachrow and Compat.eachcol

[tkf]

As eachrow and eachcol are in Compat.jl JuliaLang/Compat.jl#658, I think it makes sense to overload the functions in Compat.jl rather than creating new functions. What do you think?

I also added a test to make sure that similar overlooks do not happen in the future.

[tkf]

eachrow and eachcol need Compat 2.2: https://github.com/JuliaLang/Compat.jl/releases/tag/v2.2.0

[bkamins]

Two questions as I do not know Compat.jl well enough:

• do we have to export something we import via Compat.? (probably yes, but I just wanted to make sure)
• shoud import Compat. be used even on current versions of Julia or it should be in the if block here.

[tkf]

• do we have to export something we import via Compat.?

My understanding is that Compat is "just" a Julia package. So, if you want eachrow to work without explicitly importing Compat, I think you need to re-export eachrow from DataFrames.jl.

• shoud import Compat. be used even on current versions of Julia or it should be in the if block here.

I don't think it matters since Base.eachrow === Compat.eachrow for julia >= 1.1 and julia does not care how eachrow is imported. But my guess is that it is rather an implementation detail of julia so

if VERSION < v"1.1.0-DEV.792"
    import Base: eachcol, eachrow
else
    import Compat: eachcol, eachrow
end

makes sense if you want to play on the very safe side.

[tkf]

I pushed the change I just suggested 9f1d862. Let me know if you want to revert it.

[bkamins]

Thank you for the PR. I have left two questions to learn for the future as I do not know Compat.jl well enough.

[nalimilan]

Thanks!