Add Only transform (#230)

* Add Only transform

* Apply suggestions

* Rename variable

Author: eliascarv

docs/src/transforms.md

@@ -14,6 +14,12 @@ Select
 Reject
 ```
 
+## Only
+
+```@docs
+Only
+```
+
 ## Rename
 
 ```@docs

src/TableTransforms.jl

@@ -51,6 +51,7 @@ export
   # built-in
   Select,
   Reject,
+  Only,
   Rename,
   StdNames,
   Sort,

src/transforms.jl

@@ -265,6 +265,7 @@ end
 # ----------------
 
 include("transforms/select.jl")
+include("transforms/only.jl")
 include("transforms/rename.jl")
 include("transforms/stdnames.jl")
 include("transforms/sort.jl")

src/transforms/only.jl

@@ -0,0 +1,40 @@
+# ------------------------------------------------------------------
+# Licensed under the MIT License. See LICENSE in the project root.
+# ------------------------------------------------------------------
+
+"""
+    Only(S)
+
+Selects only columns that have scientific type `S`.
+
+# Examples
+
+```julia
+import DataScienceTraits as DST
+Only(DST.Continuous)
+```
+"""
+struct Only <: StatelessFeatureTransform
+  scitype::DataType
+  Only(S::Type{<:SciType}) = new(S)
+end
+
+isrevertible(::Type{Only}) = true
+
+function applyfeat(transform::Only, feat, prep)
+  S = transform.scitype
+  cols = Tables.columns(feat)
+  names = Tables.columnnames(cols)
+  snames = filter(names) do name
+    column = Tables.getcolumn(cols, name)
+    elscitype(column) <: S
+  end
+  strans = Select(snames)
+  newfeat, sfcache = applyfeat(strans, feat, prep)
+  newfeat, (strans, sfcache)
+end
+
+function revertfeat(::Only, newfeat, fcache)
+  strans, sfcache = fcache
+  revertfeat(strans, newfeat, sfcache)
+end

test/shows.jl

@@ -42,6 +42,20 @@
     └─ selector = [:a, :b, :c]"""
   end
 
+  @testset "Only" begin
+    T = Only(DST.Continuous)
+
+    # compact mode
+    iostr = sprint(show, T)
+    @test iostr == "Only(DataScienceTraits.Continuous)"
+
+    # full mode
+    iostr = sprint(show, MIME("text/plain"), T)
+    @test iostr == """
+    Only transform
+    └─ scitype = DataScienceTraits.Continuous"""
+  end
+
   @testset "Rename" begin
     T = Rename(:a => :x, :c => :y)
 

test/transforms.jl

@@ -1,6 +1,7 @@
 transformfiles = [
   "select.jl",
   "rename.jl",
+  "only.jl",
   "stdnames.jl",
   "sort.jl",
   "sample.jl",

test/transforms/only.jl

@@ -0,0 +1,25 @@
+@testset "Only" begin
+  @test isrevertible(Only(DST.Continuous))
+
+  a = rand(10)
+  b = rand(Float32, 10)
+  c = rand(1:9, 10)
+  d = rand('a':'z', 10)
+  t = Table(; a, b, c, d)
+
+  T = Only(DST.Continuous)
+  n, c = apply(T, t)
+  @test Tables.schema(n).names == (:a, :b)
+  @test Tables.getcolumn(n, :a) == t.a
+  @test Tables.getcolumn(n, :b) == t.b
+  tₒ = revert(T, n, c)
+  @test t == tₒ
+
+  T = Only(DST.Categorical)
+  n, c = apply(T, t)
+  @test Tables.schema(n).names == (:c, :d)
+  @test Tables.getcolumn(n, :c) == t.c
+  @test Tables.getcolumn(n, :d) == t.d
+  tₒ = revert(T, n, c)
+  @test t == tₒ
+end