Add DropExtrema transform (#201)

* Add 'DropExtrema' transform

* Add tests

* Add to docs

* Fix typo

* Update test/transforms.jl

docs/src/transforms.md

@@ -50,6 +50,12 @@ Filter
 DropMissing
 ```
 
+## DropExtrema
+
+```@docs
+DropExtrema
+```
+
 ## Map
 
 ```@docs

src/TableTransforms.jl

@@ -53,6 +53,7 @@ export
   Sample,
   Filter,
   DropMissing,
+  DropExtrema,
   Map,
   Replace,
   Coalesce,

src/transforms.jl

@@ -270,6 +270,7 @@ include("transforms/stdnames.jl")
 include("transforms/sort.jl")
 include("transforms/sample.jl")
 include("transforms/filter.jl")
+include("transforms/dropextrema.jl")
 include("transforms/map.jl")
 include("transforms/replace.jl")
 include("transforms/coalesce.jl")

src/transforms/dropextrema.jl

@@ -0,0 +1,60 @@
+# ------------------------------------------------------------------
+# Licensed under the MIT License. See LICENSE in the project root.
+# ------------------------------------------------------------------
+
+"""
+    DropExtrema(col; low=0.25, high=0.75)
+
+Drops the rows where the values in the column `col` are outside the interval
+`[quantile(col, low), quantile(col, high)]`.
+
+# Examples
+
+```julia
+DropExtrema(1)
+DropExtrema(:a, low=0.2, high=0.8)
+DropExtrema("a", low=0.3, high=0.7)
+```
+"""
+struct DropExtrema{S<:ColSpec,T} <: StatelessFeatureTransform
+  colspec::S
+  low::T
+  high::T
+
+  function DropExtrema(col::Col, low::T, high::T) where {T}
+    @assert 0 ≤ low ≤ high ≤ 1 "invalid quantiles"
+    cs = colspec(col)
+    new{typeof(cs),T}(cs, low, high)
+  end
+end
+
+DropExtrema(col::Col, low, high) = DropExtrema(col, promote(low, high)...)
+DropExtrema(col::Col; low=0.25, high=0.75) = DropExtrema(col, low, high)
+
+isrevertible(::Type{<:DropExtrema}) = true
+
+function preprocess(transform::DropExtrema, table)
+  cols = Tables.columns(table)
+  names = Tables.columnnames(cols)
+  sname = choose(transform.colspec, names) |> first
+
+  x = Tables.getcolumn(cols, sname)
+  low = convert(eltype(x), transform.low)
+  high = convert(eltype(x), transform.high)
+  xl, xh = quantile(x, (low, high))
+
+  ftrans = Filter(row -> xl ≤ row[sname] ≤ xh)
+  fprep = preprocess(ftrans, table)
+  ftrans, fprep
+end
+
+function applyfeat(::DropExtrema, feat, prep)
+  ftrans, fprep = prep
+  newfeat, ffcache = applyfeat(ftrans, feat, fprep)
+  newfeat, (ftrans, ffcache)
+end
+
+function revertfeat(::DropExtrema, newfeat, fcache)
+  ftrans, ffcache = fcache
+  revertfeat(ftrans, newfeat, ffcache)
+end

test/transforms.jl

@@ -5,6 +5,7 @@ transformfiles = [
   "sort.jl",
   "sample.jl",
   "filter.jl",
+  "dropextrema.jl",
   "map.jl",
   "replace.jl",
   "coalesce.jl",

test/transforms/dropextrema.jl

@@ -0,0 +1,47 @@
+@testset "DropExtrema" begin
+  @test isrevertible(DropExtrema(:a))
+
+  a = [6.9, 9.0, 7.8, 0.0, 5.1, 4.8, 1.1, 8.0, 5.4, 7.9]
+  b = [7.7, 4.2, 6.3, 1.4, 4.4, 0.5, 3.0, 6.1, 1.9, 1.5]
+  c = [6.1, 7.7, 5.7, 2.8, 2.8, 6.7, 8.4, 5.0, 8.9, 1.0]
+  d = [1.0, 2.8, 6.2, 1.9, 8.1, 6.2, 4.0, 6.9, 4.1, 1.4]
+  e = [1.5, 8.9, 4.1, 1.6, 5.9, 1.3, 4.9, 3.5, 2.4, 6.3]
+  f = [1.9, 2.1, 9.0, 6.2, 1.3, 8.9, 6.2, 3.8, 5.1, 2.3]
+  t = Table(; a, b, c, d, e, f)
+
+  T = DropExtrema(1)
+  n, c = apply(T, t)
+  @test n.a == [6.9, 7.8, 5.1, 5.4]
+  @test n.b == [7.7, 6.3, 4.4, 1.9]
+  @test n.c == [6.1, 5.7, 2.8, 8.9]
+  @test n.d == [1.0, 6.2, 8.1, 4.1]
+  @test n.e == [1.5, 4.1, 5.9, 2.4]
+  @test n.f == [1.9, 9.0, 1.3, 5.1]
+  tₒ = revert(T, n, c)
+  @test t == tₒ
+
+  T = DropExtrema(:c, low=0.3, high=0.7)
+  n, c = apply(T, t)
+  @test n.a == [6.9, 7.8, 4.8, 8.0]
+  @test n.b == [7.7, 6.3, 0.5, 6.1]
+  @test n.c == [6.1, 5.7, 6.7, 5.0]
+  @test n.d == [1.0, 6.2, 6.2, 6.9]
+  @test n.e == [1.5, 4.1, 1.3, 3.5]
+  @test n.f == [1.9, 9.0, 8.9, 3.8]
+  tₒ = revert(T, n, c)
+  @test t == tₒ
+
+  T = DropExtrema("e", low=0.2, high=0.8)
+  n, c = apply(T, t)
+  @test n.a == [7.8, 0.0, 5.1, 1.1, 8.0, 5.4]
+  @test n.b == [6.3, 1.4, 4.4, 3.0, 6.1, 1.9]
+  @test n.c == [5.7, 2.8, 2.8, 8.4, 5.0, 8.9]
+  @test n.d == [6.2, 1.9, 8.1, 4.0, 6.9, 4.1]
+  @test n.e == [4.1, 1.6, 5.9, 4.9, 3.5, 2.4]
+  @test n.f == [9.0, 6.2, 1.3, 6.2, 3.8, 5.1]
+  tₒ = revert(T, n, c)
+  @test t == tₒ
+
+  # throws
+  @test_throws AssertionError DropExtrema(:a, low=0, high=1.4)
+end