From 4f21ce4473be02def6cfee43763b83871bf97d5f Mon Sep 17 00:00:00 2001
From: rofinn <rory.finnegan@gmail.com>
Date: Tue, 25 Jun 2019 13:07:10 -0500
Subject: [PATCH] Fix linear interp behaviour when interpolating between
 identical points and test end interpolation behaviour.

---
 Project.toml           | 15 +++++++++++++++
 src/imputors/interp.jl | 14 ++++++--------
 test/runtests.jl       | 12 ++++++++++++
 3 files changed, 33 insertions(+), 8 deletions(-)
 create mode 100644 Project.toml

diff --git a/Project.toml b/Project.toml
new file mode 100644
index 0000000..7ffdf35
--- /dev/null
+++ b/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"]
diff --git a/src/imputors/interp.jl b/src/imputors/interp.jl
index 7a4b0af..a2a8c92 100644
--- a/src/imputors/interp.jl
+++ b/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
diff --git a/test/runtests.jl b/test/runtests.jl
index 3d8754d..1a268e5 100644
--- a/test/runtests.jl
+++ b/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