`discretediag`'s signature should imo be restricted to Integer

[penelopeysm]

MCMCDiagnosticTools.jl/src/discretediag.jl

Lines 438 to 440 in 1570ce9

	function discretediag(
	chains::AbstractArray{<:Real,3}; frac::Real=0.3, method::Symbol=:weiss, nsim::Int=1000
	)

The type AbstractArray{3,Real} here is too broad: inside the helper function discretediag_sub, it immediately gets converted to Int anyway.

MCMCDiagnosticTools.jl/src/discretediag.jl

Lines 387 to 389 in 1570ce9

	for j in 1:num_vars
	X = convert(AbstractMatrix{Int}, c[:, :, j])
	result = diag_all(X, method, nsim, start_iter, step_size)

Technically, there isn't any wrong behaviour going on here because non-integer data will error, but it is probably a more confusing error than necessary (see below). It would probably be shorter and easier to parse if it was a MethodError saying that Array{3,Float64} is not accepted, available methods are Array{3,Integer}.

If the motivation for the signature is to work around MCMCChains's overly aggressive conversion to Float, then I think a better place to handle that would be the MCMCChains overload here?

Said stack trace:

ERROR: InexactError: Int64(-0.2146900723338993)
Stacktrace:
  [1] Int64
    @ ./float.jl:994 [inlined]
  [2] convert
    @ ./number.jl:7 [inlined]
  [3] setindex!
    @ ./genericmemory.jl:243 [inlined]
  [4] unsafe_copyto!(dest::Memory{Int64}, doffs::Int64, src::Memory{Float64}, soffs::Int64, n::Int64)
    @ Base ./genericmemory.jl:153
  [5] unsafe_copyto!
    @ ./genericmemory.jl:133 [inlined]
  [6] _copyto_impl!
    @ ./array.jl:308 [inlined]
  [7] copyto!
    @ ./array.jl:294 [inlined]
  [8] copyto!
    @ ./array.jl:319 [inlined]
  [9] copyto_axcheck!
    @ ./abstractarray.jl:1167 [inlined]
 [10] AbstractMatrix{Int64}(A::Matrix{Float64})
    @ Base ./array.jl:627
 [11] convert
    @ ./abstractarray.jl:18 [inlined]
 [12] discretediag_sub(c::PermutedDimsArray{…}, frac::Float64, method::Symbol, nsim::Int64, start_iter::Int64, step_size::Int64)
    @ MCMCDiagnosticTools ~/.julia/packages/MCMCDiagnosticTools/wE49x/src/discretediag.jl:388
 [13] discretediag(chains::PermutedDimsArray{…}; frac::Float64, method::Symbol, nsim::Int64)
    @ MCMCDiagnosticTools ~/.julia/packages/MCMCDiagnosticTools/wE49x/src/discretediag.jl:448
 [14] discretediag(chains::PermutedDimsArray{Float64, 3, (1, 3, 2), (1, 3, 2), Array{Float64, 3}})
    @ MCMCDiagnosticTools ~/.julia/packages/MCMCDiagnosticTools/wE49x/src/discretediag.jl:438
 [15] discretediag(chains::Chains{…}; sections::Symbol, kwargs::@Kwargs{})
    @ MCMCChains ~/.julia/packages/MCMCChains/vqJuv/src/discretediag.jl:16
 [16] discretediag(chains::Chains{Float64, AxisArrays.AxisArray{…}, Missing, @NamedTuple{…}, @NamedTuple{…}})
    @ MCMCChains ~/.julia/packages/MCMCChains/vqJuv/src/discretediag.jl:7
 [17] top-level scope
    @ REPL[14]:1
Some type information was truncated. Use `show(err)` to see complete types.