knuths_sample! is incorrect when used with offset axes

[yurivish]

The function knuths_sample! is documented here.

julia> StatsBase.knuths_sample!(OffsetArray(collect(1:11), -5:5), zeros(11))
11-element Array{Float64,1}:
      7.0
 559108.0
      0.0
      0.0
      4.557992976e9
     10.0
     11.0
     11.0
      9.0
      8.0
      4.417700624e9

The behavior is due to multiple incorrect uses of @inbounds.

StatsBase.jl/src/sampling.jl

Lines 88 to 117 in 0ffe2e2

	function knuths_sample!(rng::AbstractRNG, a::AbstractArray, x::AbstractArray;
	initshuffle::Bool=true)
	n = length(a)
	k = length(x)
	k <= n || error("length(x) should not exceed length(a)")
	# initialize
	for i = 1:k
	@inbounds x[i] = a[i]
	end
	if initshuffle
	@inbounds for j = 1:k
	l = rand(rng, j:k)
	if l != j
	t = x[j]
	x[j] = x[l]
	x[l] = t
	end
	end
	end
	# scan remaining
	s = Sampler(rng, 1:k)
	for i = k+1:n
	if rand(rng) * i < k # keep it with probability k / i
	@inbounds x[rand(rng, s)] = a[i]
	end
	end
	return x
	end

[devmotion]

This was fixed a while ago by #833:

julia> StatsBase.knuths_sample!(OffsetArray(collect(1:11), -5:5), zeros(11))
ERROR: ArgumentError: non 1-based arrays are not supported
Stacktrace:
 [1] knuths_sample!(rng::Random.TaskLocalRNG, a::OffsetVector{Int64, Vector{Int64}}, x::Vector{Float64}; initshuffle::Bool)
   @ StatsBase ~/.julia/packages/StatsBase/NuJjt/src/sampling.jl:145
 [2] knuths_sample!
   @ ~/.julia/packages/StatsBase/NuJjt/src/sampling.jl:143 [inlined]
 [3] knuths_sample!(a::OffsetVector{Int64, Vector{Int64}}, x::Vector{Float64})
   @ StatsBase ~/.julia/packages/StatsBase/NuJjt/src/sampling.jl:177
 [4] top-level scope
   @ REPL[18]:1