Fix #19: constant columns in Scale and Quantile

Author: juliohm

Diff for: src/distributions.jl

@@ -41,8 +41,8 @@ function cdf(d::EmpiricalDistribution{T}, x::T) where {T<:Real}
   elseif x > u
     return one(T)
   else
-    if head == tail
-      return head / n
+    if l == u
+      return tail / n
     else
       pl, pu = head / n, tail / n
       return (pu - pl) * (x - l) / (u - l) + pl

Diff for: src/transforms/scale.jl

@@ -27,6 +27,7 @@ isrevertible(::Type{Scale}) = true
 function colcache(transform::Scale, x)
   levels = (transform.low, transform.high)
   xl, xh = quantile(x, levels)
+  xl == xh && ((xl, xh) = (zero(xl), one(xh)))
   (xl=xl, xh=xh)
 end
 

Diff for: test/transforms.jl

@@ -219,6 +219,17 @@
   end
 
   @testset "Scale" begin
+    # constant column
+    x = fill(3.0, 10)
+    y = rand(10)
+    t = Table(; x, y)
+    T = MinMax()
+    n, c = apply(T, t)
+    @test n.x == x
+    @test n.y != y
+    tₒ = revert(T, n, c)
+    @test tₒ == t
+
     Random.seed!(42) # to reproduce the results
     x = rand(Normal(4,3), 4000)
     y = rand(Normal(7,5), 4000)
@@ -274,6 +285,17 @@
     r = revert(Quantile(), n, c)
     @test all(-4 .< extrema(n.z) .< 4)
     @test all(0 .≤ extrema(r.z) .≤ 1)
+
+    # constant column
+    x = fill(3.0, 10)
+    y = rand(10)
+    t = Table(; x, y)
+    T = Quantile()
+    n, c = apply(T, t)
+    @test maximum(abs, n.x - x) < 0.1
+    @test n.y != y
+    tₒ = revert(T, n, c)
+    @test tₒ.x == t.x
   end
 
   @testset "Functional" begin