tryparse should have argument to return missing

[s-celles]

Hello,

Following JuliaData/DataFrames.jl#1854 I wonder if tryparse implementation shouldn't have an argument to output missing instead of nothing.

So it will be possible to simply do

julia> using DataFrames
julia> df = DataFrame(:A=>["", "2", "3"], :B=>[1.1, 2.2, 3.3])
3×2 DataFrame
│ Row │ A      │ B       │
│     │ String │ Float64 │
├─────┼────────┼─────────┤
│ 1   │        │ 1.1     │
│ 2   │ 2      │ 2.2     │
│ 3   │ 3      │ 3.3     │
julia> df.A = tryparse.(Int, df.A, missing)
3-element Array{Union{Missing, Int64},1}:
  missing
 2
 3
julia> df
3×2 DataFrame
│ Row │ A       │ B       │
│     │ Int64⍰  │ Float64 │
├─────┼─────────┼─────────┤
│ 1   │ missing │ 1.1     │
│ 2   │ 2       │ 2.2     │
│ 3   │ 3       │ 3.3     │

Your opinion?

Kind regards

[KristofferC]

The value is not missing here. If you want missing just wrap tryparse in a function that transform nothing to missing.

[quinnj]

Yeah, this should be as simple as doing mytryparse(T, str) = something(tryparse(T, str), missing)

[s-celles]

Maybe the discussion should continue in JuliaData/Missings.jl#61

[ghost]

Julia Version 1.5.4
Commit 69fcb5745b (2021-03-11 19:13 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin18.7.0)
  CPU: Intel(R) Xeon(R) W-3275M CPU @ 2.50GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, skylake-avx512)

using

mytryparse(T, str) = something(tryparse(T, str), missing)
mytryparse(Int, missing)

throws

MethodError: no method matching tryparse(::Type{Int64}, ::Missing)
Closest candidates are:
  tryparse(::Type{T}, ::AbstractString; base) where T<:Integer at parse.jl:232

Stacktrace:
 [1] mytryparse(::Type{T} where T, ::Missing) at ./In[138]:1
 [2] top-level scope at In[139]:1
 [3] include_string(::Function, ::Module, ::String, ::String) at ./loading.jl:1091

I referred to https://discourse.julialang.org/t/i-have-a-dataframe-with-multiple-columns-of-type-union-missing-string-what-is-the-most-concise-manner-of-converting-the-non-missing-values-in-float/54205