Add 'Unit' transform

Author: eliascarv

docs/src/transforms.md

@@ -116,6 +116,12 @@ AbsoluteUnits
 Unitify
 ```
 
+## Unit
+
+```@docs
+Unit
+```
+
 ## Map
 
 ```@docs

src/TableTransforms.jl

@@ -67,6 +67,7 @@ export
   DropUnits,
   AbsoluteUnits,
   Unitify,
+  Unit,
   Map,
   Replace,
   Coalesce,

src/transforms.jl

@@ -281,6 +281,7 @@ include("transforms/dropunits.jl")
 include("transforms/dropconstant.jl")
 include("transforms/absoluteunits.jl")
 include("transforms/unitify.jl")
+include("transforms/unit.jl")
 include("transforms/map.jl")
 include("transforms/replace.jl")
 include("transforms/coalesce.jl")

src/transforms/unit.jl

@@ -0,0 +1,75 @@
+# ------------------------------------------------------------------
+# Licensed under the MIT License. See LICENSE in the project root.
+# ------------------------------------------------------------------
+
+"""
+    Unit(unit)
+
+TODO
+
+    Unit(cols₁ => unit₁, cols₂ => unit₂, ..., colsₙ => unitₙ)
+
+TODO
+
+# Examples
+
+```julia
+```
+"""
+struct Unit <: StatelessFeatureTransform
+  selectors::Vector{ColumnSelector}
+  units::Vector{Units}
+end
+
+Unit() = throw(ArgumentError("cannot create Unit transform without arguments"))
+
+Unit(unit::Units) = Unit([AllSelector()], [unit])
+
+Unit(pairs::Pair...) = Unit(collect(selector.(first.(pairs))), collect(last.(pairs)))
+
+isrevertible(::Type{<:Unit}) = true
+
+function applyfeat(transform::Unit, feat, prep)
+  cols = Tables.columns(feat)
+  names = Tables.columnnames(cols)
+
+  selectors = transform.selectors
+  units = transform.units
+  pairs = mapreduce(vcat, selectors, units) do selector, u
+    snames = selector(names)
+    snames .=> u
+  end
+  unitdict = Dict(pairs) 
+
+  tuples = map(names) do name
+    x = Tables.getcolumn(cols, name)
+    if haskey(unitdict, name)
+      u = unitdict[name]
+      y = uconvert.(u, x)
+      (y, unit(eltype(x)))
+    else
+      (x, nothing)
+    end
+  end
+
+  columns = first.(tuples)
+  ounits = last.(tuples)
+
+  𝒯 = (; zip(names, columns)...)
+  newfeat = 𝒯 |> Tables.materializer(feat)
+  newfeat, ounits
+end
+
+function revertfeat(::Unit, newfeat, fcache)
+  cols = Tables.columns(newfeat)
+  names = Tables.columnnames(cols)
+
+  ounits = fcache
+  columns = map(names, ounits) do name, u
+    x = Tables.getcolumn(cols, name)
+    isnothing(u) ? x : uconvert.(u, x)
+  end
+
+  𝒯 = (; zip(names, columns)...)
+  𝒯 |> Tables.materializer(newfeat)
+end