Prevent overflow in mean(::AbstractRange) and relax type constraint

[vyu]

Currently, mean(::AbstractRange) can overflow:

julia> using Statistics

julia> mean(typemax(Int):typemax(Int))
-1.0

julia> mean(prevfloat(Inf):prevfloat(Inf))
Inf

This PR prevents this overflow.

In addition, I've relaxed the type constraint from AbstractRange{<:Real} to AbstractRange{<:Any}, since the computation here is correct for any type that implements addition and numerical division (unlike the median, which requires an order). Currently, the mean of non-real ranges falls back to mean(::AbstractVector), which also requires addition and numerical division.

In line with this, oftype([...], NaN) is changed to zero(T)/0 so that mean(LinRange(2im, 1im, 0)) is NaN + NaN*im (consistent with mean(ComplexF64[])) instead of NaN + 0.0im.

[ararslan]

Suggested change

	return first(r)/2 + last(r)/2
	return middle(r)

This method is already defined appropriately for ranges and behaves as desired when the input is non-empty:

julia> middle(typemax(Int):typemax(Int)) ≈ typemax(Int)
true

[vyu]

It would be less performant to call middle because it currently doesn't elide bounds checks and a[end] is unfortunately slow for StepRange (it calls lastindex, which calls length, which requires a division). In contrast, first and last simply accesses fields of the range struct (except for StepRangeLen).

I've just opened a PR (#116) to have middle call mean instead. Would you mind taking a look?

[nalimilan]

Given that both mean here and middle at #116 check that the input is not empty, better not have one call the other and instead duplicate the (very short) computation?

[vyu]

Sure, sounds good to me. I'll update #116 to not call mean.

[ararslan]

Thanks for the PR! Great first contribution to the package. 🙂

[nalimilan]

Do you want to finish this @vyu?

[codecov-commenter]

Codecov Report

Base: 96.93% // Head: 96.93% // No change to project coverage 👍

Coverage data is based on head (6c66b96) compared to base (576db0f).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #115   +/-   ##
=======================================
  Coverage   96.93%   96.93%           
=======================================
  Files           1        1           
  Lines         424      424           
=======================================
  Hits          411      411           
  Misses         13       13           

Impacted Files	Coverage Δ
src/Statistics.jl	96.93% <100.00%> (ø)

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[Jay-sanjay]

Hello , what is the status of this issue is it solved............
I would be happy to work for it

[nalimilan]

Thanks for proposing your help. I think you can start from the current state of the PR and the last round of comments. You probably won't be able to push to this branch but you can start a new PR and post a link here.

[nalimilan]

Closing in favor of #150.