Feature request: creating new columns as in DataFrames

[hurak]

Reading that TSFrames.jl aims to provide the convenience of Dataframes.jl, I was wondering if it could be possible to make the following functionality of creating a new column work:

First, we create a DataFrame and a TSFrame:

julia> using DataFrames

julia> using TSFrames

julia> d = Date(2025,1,1):Day(1):Date(2025,1,3)
Date("2025-01-01"):Day(1):Date("2025-01-03")

julia> df = DataFrame(Date=d, Value=1:3)
3×2 DataFrame
 Row │ Date        Value 
     │ Date        Int64 
─────┼───────────────────
   1 │ 2025-01-01      1
   2 │ 2025-01-02      2
   3 │ 2025-01-03      3

julia> ts = TSFrame(1:3, d)
3×1 TSFrame with Date Index
 Index       x1    
 Date        Int64 
───────────────────
 2025-01-01      1
 2025-01-02      2
 2025-01-03      3

Now we create a new column within the DataFrame

julia> df[!, :New_column] .= 0.0
3-element Vector{Float64}:
 0.0
 0.0
 0.0

julia> df
3×3 DataFrame
 Row │ Date        Value  New_column 
     │ Date        Int64  Float64    
─────┼───────────────────────────────
   1 │ 2025-01-01      1         0.0
   2 │ 2025-01-02      2         0.0
   3 │ 2025-01-03      3         0.0

It works fine. We try to do something similar with the TSFrame:

julia> ts[!, :New_column] .= 0.0
ERROR: MethodError: no method matching getindex(::TSFrame, ::typeof(!), ::Symbol)
The function `getindex` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  getindex(::TSFrame, ::Colon, ::Union{String, Symbol})
   @ TSFrames ~/.julia/packages/TSFrames/OTvKe/src/getindex.jl:479
  getindex(::TSFrame, ::Int64, ::Union{String, Symbol})
   @ TSFrames ~/.julia/packages/TSFrames/OTvKe/src/getindex.jl:259
  getindex(::TSFrame, ::T, ::Union{String, Symbol}) where T<:TimeType
   @ TSFrames ~/.julia/packages/TSFrames/OTvKe/src/getindex.jl:268

Indeed, somehow as a new user I had the impression that the TSFrame type is just the DataFrame with the special first (index) column. And then I felt tempted to apply the tricks applicable for DataFrames.

[chiraganand]

TSFrames currently doesn't support column addition directly but you are right a TSFrame is, essentially, a DataFrame underneath with an Index column. You can access the DataFrame object by ts.coredata so this should work:

julia> ts.coredata[!, :New_column] .= 0.0

As long as you don't modify the Index column manually (including changing the sorting order) things should be okay.