Fix linear interp behaviour when interpolating between identical poin…

…ts and test end interpolation behaviour.

Project.toml

@@ -0,0 +1,15 @@
+name = "Impute"
+uuid = "f7bf1975-0170-51b9-8c5f-a992d46b9575"
+authors = ["Invenia Technical Computing"]
+version = "0.2.0"
+
+[deps]
+DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
+Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
+
+[extras]
+RDatasets = "ce6b1742-4840-55fa-b093-852dadbb1d8b"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[targets]
+test = ["RDatasets", "Test"]

src/imputors/interp.jl

@@ -27,16 +27,14 @@ function impute!(imp::Interpolate, ctx::Context, data::AbstractVector{<:Union{T,
 
                 diff = data[next_idx] - data[prev_idx]
                 incr = diff / T(gap_sz + 1)
-                start_val = data[prev_idx]
-                stop_val = data[next_idx]
+                val = data[prev_idx] + incr
 
-                values = Real(start_val):Real(incr):Real(stop_val)
+                # Iteratively fill in the values
+                for j in i:(next_idx - 1)
+                    data[j] = val
+                    val += incr
+                end
 
-                idx_range = prev_idx:(prev_idx + length(values) - 1)
-                # println(collect(idx_range))
-                # println(values)
-
-                data[idx_range] = values
                 i = next_idx
             else
                 break

test/runtests.jl

@@ -21,6 +21,18 @@ using Statistics
         result = impute(a, :interp; limit=0.2)
         @test result == collect(1.0:1.0:20)
         @test result == interp(a)
+
+        # Test interpolation between identical points
+        b = ones(Union{Float64, Missing}, 20)
+        b[[2, 3, 7]] .= missing
+        @test interp(b) == ones(Union{Float64, Missing}, 20)
+
+        # Test interpolation at endpoints
+        b = ones(Union{Float64, Missing}, 20)
+        b[[1, 3, 20]] .= missing
+        result = interp(b)
+        @test ismissing(result[1])
+        @test ismissing(result[20])
     end
 
     @testset "Fill" begin