# Using Weights from statsbase in Julia, and using an array

**URL:** <https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820>\
**Category:** New to Julia\
**Tags:** package\
**Created:** [November 26, 2020, 2:58pm UTC](https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820 "2020-11-26T14:58:39Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![naturalmechanics](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/naturalmechanics/32/20561_2.png) [@naturalmechanics](https://discourse.julialang.org/u/naturalmechanics)\
**Post date:** [November 26, 2020, 2:58pm UTC](https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820/1 "2020-11-26T14:58:39Z")

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Hi I am new to Julia, and I am trying to play with it a bit.

Consider this function:

```julia
function drawValues(fromDistribution, byCount)

#=
inputs:
fromDistribution : 
    A 2D array
    Each element is an array with two elements
    The first one is a value, and the second one is the probability of that value
    We will draw a value out of this distribution from a random number generator
    
byCount :
    An integer
    We draw that many values from the source distribution

=#

values = []
wts = []

for i = 1:length(fromDistribution)
    
    push!(values, fromDistribution[i][1])
    push!(wts , fromDistribution[i][2])
    
end

w = Weights(wts)

res = []

for i = 1:byCount
    
    r = sample(values, w)
    push!(res, r)
    
end

plot(values, wts)
print(res)

end

```

This throws the error :

> ERROR: MethodError: no method matching Weights(::Array{Any,1}, ::Float64) Closest candidates are: Weights(::var"#18#V", ::var"#16#S") where {var"#16#S"\<:Real, var"#17#T"\<:Real, var"#18#V"\<:AbstractArray{var"#17#T",1}} at /home/hedgehog/.julia/packages/StatsBase/EA8Mh/src/weights.jl:13  
> Weights(::Any) at /home/hedgehog/.julia/packages/StatsBase/EA8Mh/src/weights.jl:16 Stacktrace: [1] Weights(::Array{Any,1}) at /home/hedgehog/.julia/packages/StatsBase/EA8Mh/src/weights.jl:16 [2] drawValues(::Array{Array{Float64,1},1}, ::Int64) at /home/hedgehog/LASER.jl:51 [3] top-level scope at REPL[13]:1 [4] run\_repl(::REPL.AbstractREPL, ::Any) at /build/julia/src/julia-1.5.3/usr/share/julia/stdlib/v1.5/REPL/src/REPL.jl:288

It seems, that the second definition ( `Weights(::Array{Any,1})` ) whould fit. But somehow Julia sees two input arguments?

Please help.

Versioninfo :

> Julia Version 1.5.3  
> Commit 788b2c77c1\* (2020-11-09 13:37 UTC)  
> Platform Info:  
> OS: Linux (x86\_64-pc-linux-gnu)  
> CPU: AMD Ryzen 7 3700X 8-Core Processor  
> WORD\_SIZE: 64  
> LIBM: libopenlibm  
> LLVM: libLLVM-10.0.1 (ORCJIT, znver2)

---

<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [November 26, 2020, 8:16pm UTC](https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820/2 "2020-11-26T20:16:58Z")

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Welcome to the community! When posting it is generally helpful to make your example self contained, so that other people can reproduce the error you’re seeing. In this case, I assume this would have meant including the packages you are using (`StatsBase`?) as well as an example of how you construct `fromDistribution`.

I assume this is a learning exercise, as sampling `n` values from a collection with weights `w` is already implemented in StatsBase:

```julia
julia> using StatsBase

julia> sample(1:10, Weights(rand(10)), 5)
5-element Vector{Int64}:
 5
 6
 1
 2
 6

```

Without being able to run your code though I think your problem is (maybe somewhat confusingly) that you are using an untyped array `Any` to construct your weights. Consider:

```julia
julia> Weights([1,2,3])
3-element Weights{Int64, Int64, Vector{Int64}}:
 1
 2
 3

julia> Weights(Any[1, 2, 3])
ERROR: MethodError: no method matching Weights(::Vector{Any}, ::Int64)
Closest candidates are:
  Weights(::var"#6#V", ::var"#4#S") where {var"#4#S"<:Real, var"#5#T"<:Real, var"#6#V"<:AbstractVector{var"#5#T"}} at /home/nils/.julia/packages/StatsBase/EA8Mh/src/weights.jl:13
  Weights(::Any) at /home/nils/.julia/packages/StatsBase/EA8Mh/src/weights.jl:16
Stacktrace:
 [1] Weights(vs::Vector{Any})
   @ StatsBase ~/.julia/packages/StatsBase/EA8Mh/src/weights.jl:16
 [2] top-level scope
   @ none:1

```

In the first example, I use a vector of `Int64` (Julia infers the type automatically when constructing the array, as all elements are `Int64`), while in the second example I force the array to be of type `Any`. This is what you are implicitly doing when you instantiate your `wts` vector with `[]`:

```julia
julia> []
Any[]

```

`push!`ing to this afterwards won’t change the type of the container, so you end up passing a `Vector{Any}` to the weights constructor, which fails as you see above.

I’m not all that familiar with the internals of `StatsBase`, but it seems the confusion comes from `Weights(::Array{Any, 1})` being allowed, but then calling `Weights(<:AbstractVector{T}, <:Real)` in the next step, so the method error is one step removed from the call that the user makes. You can see this in the source when you do `@edit Weights(wts)`, but again it’s a bit opaque as the constructor itself is created from a macro.

---

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**Author:** ![nalimilan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nalimilan/32/147_2.png) [@nalimilan](https://discourse.julialang.org/u/nalimilan)\
**Post date:** [November 27, 2020, 12:34pm UTC](https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820/3 "2020-11-27T12:34:33Z")

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> [@naturalmechanics](#):
>
> It seems, that the second definition ( `Weights(::Array{Any,1})` ) whould fit. But somehow Julia sees two input arguments?

Actually there’s no `Weights(::Array{Any,1})`. What you see in the stacktrace is the fact that _you_ passed an `Array{Any}` to the `Weigths(::Any)` method. But I agree this would be clearer if the single-argument method throwed the error. See:

> <https://github.com/JuliaStats/StatsBase.jl/pull/620>
>
> This ensures the error is thrown earlier for clarity, instead of doing it from t…he two-argument constructor.
> 
> See https://discourse.julialang.org/t/using-weights-from-statsbase-in-julia-and-using-an-array/50820.