[Feature request] Support for converting single-column dataframes to Vectors

[jakewilliami]

This might not be that useful—maybe it is just me that would like this. Let me know what you think (example below).

julia> df = DataFrame(A = [1, 2, 3, 4])
4×1 DataFrame
│ Row │ A     │
│     │ Int64 │
├─────┼───────┤
│ 1   │ 1     │
│ 2   │ 2     │
│ 3   │ 3     │
│ 4   │ 4     │

julia> Vector(df)
ERROR: MethodError: no method matching Array{T,1} where T(::DataFrame)
  ...

julia> function Vector(df::DataFrame)
       if isone(ncol(df))
       return vec(Matrix(df))
       else
       error("Cannot convert a multi-column dataframe to a vector.")
       end
       end
Array{T,1} where T

julia> Vector(df)
4-element Array{Int64,1}:
 1
 2
 3
 4

[bkamins]

This fails for matrices:

julia> x = rand(2,2)
2×2 Array{Float64,2}:
 0.965899  0.90723
 0.653601  0.99919

julia> Vector(x)
ERROR: MethodError: no method matching Array{T,1} where T(::Array{Float64,2})

so I think it should fail for data frames.

A more natural pattern to get what you want is:

only(eachcol(df))

with the only difference that it will not copy the extracted vector as opposed to your proposal.