### Author:  [@kevbonham](https://discourse.julialang.org/u/kevbonham)
#### Post date: [March 6, 2017, 1:36am UTC](https://discourse.julialang.org/t/sample-from-a-data-vector-with-na-values/2482/1 "2017-03-06T01:36:15Z")
Is there a way to use `sample()` function from a `DataArray` in a way that deals gracefully with `NA` values?
What I mean is that if I do `sample(a)`, it works fine - sometimes returning a `Float64`, and sometimes returning NA. But when I add a number (eg `sample(a, 5)`, it works if all the samples are `Float64`s or if they’re all `NA`s, but if it gets a mix (i assume), I get:
```julia
MethodError: cannot `convert` an object of type DataArrays.NAtype to an object of type Float64
```
Is there anyway around this (so that my sample can have both `Float64` and `NA` values)?
EDIT: whole error message:
```julia
MethodError: Cannot `convert` an object of type DataArrays.NAtype to an object of type Float64
This may have arisen from a call to the constructor Float64(...),
since type constructors fall back to convert methods.
in setindex!(::Array{Float64,1}, ::DataArrays.NAtype, ::Int64) at array.jl:415
in direct_sample!(::DataArrays.DataArray{Float64,1}, ::Array{Float64,1}) at sampling.jl:35
in #sample!#66(::Bool, ::Bool, ::Function, ::DataArrays.DataArray{Float64,1}, ::Array{Float64,1}) at sampling.jl:280
in (::StatsBase.#kw##sample!)(::Array{Any,1}, ::StatsBase.#sample!, ::DataArrays.DataArray{Float64,1}, ::Array{Float64,1}) at :0
in sample(::DataArrays.DataArray{Float64,1}, ::Int64) at sampling.jl:318
in include_string(::String, ::String) at loading.jl:441
in include_string(::String, ::String, ::Int64) at eval.jl:28
in include_string(::Module, ::String, ::String, ::Int64, ::Vararg{Int64,N}) at eval.jl:32
in (::Atom.##53#56{String,Int64,String})() at eval.jl:40
in withpath(::Atom.##53#56{String,Int64,String}, ::String) at utils.jl:30
in withpath(::Function, ::String) at eval.jl:46
in macro expansion at eval.jl:57 [inlined]
in (::Atom.##52#55{Dict{String,Any}})() at task.jl:60
```
---
### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [March 6, 2017, 2:19am UTC](https://discourse.julialang.org/t/sample-from-a-data-vector-with-na-values/2482/2 "2017-03-06T02:19:49Z")
You didn’t report the whole error message. To which type is it trying to `convert`?
What should `sample()` return if it hits an `NA`?
---
### Author:  [@mkborregaard](https://discourse.julialang.org/u/mkborregaard)
#### Post date: [March 6, 2017, 7:54am UTC](https://discourse.julialang.org/t/sample-from-a-data-vector-with-na-values/2482/3 "2017-03-06T07:54:57Z")
I don’t think so, but you can do it with the new NullableArrays data format.
---
### Author:  [@mbauman](https://discourse.julialang.org/u/mbauman)
#### Post date: [March 6, 2017, 8:20am UTC](https://discourse.julialang.org/t/sample-from-a-data-vector-with-na-values/2482/4 "2017-03-06T08:20:45Z")
`sample` constructs an output `Vector{T}` using the `eltype` of the input. You can use the in-place mutating `sample!` instead, and provide your own `DataArray`:
```julia
julia> sample!(a, similar(a, 5)) # Note the argument order; output comes second here
5-element DataArrays.DataArray{Int64,1}:
…
```
Perhaps changing `sample` to use `similar` internally would be generally useful.
---
### Author:  [@kevbonham](https://discourse.julialang.org/u/kevbonham)
#### Post date: [March 6, 2017, 1:31pm UTC](https://discourse.julialang.org/t/sample-from-a-data-vector-with-na-values/2482/5 "2017-03-06T13:31:11Z")
> You can use the in-place mutating sample! instead, and provide your own DataArray
This works perfectly, thanks!
I agree that this would be useful generally, but I’m not sure what other implications this has. Perhaps just a note in the docs mentioning this work-around would be sufficient - this strikes me as something that could trip up more than just me. It was particularly odd that it worked sometimes (if none of the samples were `NA` )