Simple implementation of KNN imputation

* inspired by SVD imputation (invenia#16)

Manifest.toml

@@ -0,0 +1,152 @@
+# This file is machine-generated - editing it directly is not advised
+
+[[Base64]]
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+[[Combinatorics]]
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+[[DataValueInterfaces]]
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+[[Distances]]
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+[[Distributed]]
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+
+[[InteractiveUtils]]
+deps = ["Markdown"]
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+[[IterTools]]
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+[[IteratorInterfaceExtensions]]
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+[[LinearAlgebra]]
+deps = ["Libdl"]
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+[[Missings]]
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+
+[[NearestNeighbors]]
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+[[StatsBase]]
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+[[Tables]]
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+[[Test]]
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+
+[[Unicode]]
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Project.toml

@@ -4,7 +4,9 @@ authors = ["Invenia Technical Computing"]
 version = "0.4.0"
 
 [deps]
+Distances = "b4f34e82-e78d-54a5-968a-f98e89d6e8f7"
 IterTools = "c8e1da08-722c-5040-9ed9-7db0dc04731e"
+NearestNeighbors = "b8a86587-4115-5ab1-83bc-aa920d37bbce"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 StatsBase = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"
@@ -20,10 +22,11 @@ julia = "1"
 
 [extras]
 AxisArrays = "39de3d68-74b9-583c-8d2d-e117c070f3a9"
+Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 RDatasets = "ce6b1742-4840-55fa-b093-852dadbb1d8b"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["AxisArrays", "DataFrames", "Dates", "RDatasets", "Test"]
+test = ["AxisArrays", "Combinatorics", "DataFrames", "Dates", "RDatasets", "Test"]

src/Impute.jl

@@ -1,6 +1,8 @@
 module Impute
 
+using Distances
 using IterTools
+using NearestNeighbors
 using Random
 using Statistics
 using StatsBase
@@ -63,6 +65,7 @@ const global imputation_methods = (
     locf = LOCF,
     nocb = NOCB,
     srs = SRS,
+    knn = KNN,
 )
 
 include("deprecated.jl")

src/imputors.jl

@@ -167,6 +167,6 @@ function impute!(table, imp::Imputor)
 end
 
 
-for file in ("drop.jl", "locf.jl", "nocb.jl", "interp.jl", "fill.jl", "chain.jl", "srs.jl")
+for file in ("drop.jl", "locf.jl", "nocb.jl", "interp.jl", "fill.jl", "chain.jl", "srs.jl", "knn.jl")
     include(joinpath("imputors", file))
 end

src/imputors/knn.jl

@@ -0,0 +1,79 @@
+"""
+    KNN <: Imputor
+
+Imputation using k-Nearest Neighbor algorithm.
+
+# Keyword Arguments
+* `num_nn::Int`: number of nearest neighbors
+* `dist::MinkowskiMetric`: distance metric suppports by `NearestNeighbors.jl` (Euclidean, Chebyshev, Minkowski and Cityblock)
+* `on_complete::Function`: a function to run when imputation is complete
+
+# Reference
+* Troyanskaya, Olga, et al. "Missing value estimation methods for DNA microarrays." Bioinformatics 17.6 (2001): 520-525.
+"""
+# TODO : Support Categorical Distance (NearestNeighbors.jl support needed)
+struct KNN{M} <: Imputor where M <: NearestNeighbors.MinkowskiMetric
+    num_nn::Int
+    dist::M
+    context::AbstractContext
+end
+
+function KNN(; num_nn=1,
+    dist=Euclidean(), context=Context())
+
+    KNN(num_nn, dist, context)
+end
+
+"""
+    impute!(imp::KNN, data::AbstractMatrix)
+
+data : N x D matrix
+"""
+function impute!(data::AbstractMatrix{<:Union{T, Missing}},
+    imp::KNN) where T<:Real
+
+    imp.context() do ctx
+        # Get our before and after views of our missing and non-missing data
+        mmask = ismissing.(data)
+        omask = .!mmask
+
+        mdata = data[mmask]
+        odata = data[omask]
+
+        # Fill in the original data as mean value
+        # TODO : pass Fill in constructor
+        impute!(data, Fill(; value=mean, context=ctx))
+
+        # transpose to D x N for KDTree
+        dataT = float.(collect(transpose(data)))
+        kdtree = KDTree(dataT, imp.dist)
+
+        # index of columns
+        idxs, dists = NearestNeighbors.knn(kdtree, dataT, imp.num_nn, true)
+        invWdist(i) = dists[i] == 0 ? dataT[idxs[i]] : dists[i]
+        # TODO : going to parallel?
+        for (i, x) in enumerate(mdata)
+            if ndims(dataT) != 1
+                # ndims(dataT) == 1 means there is there is only single row.
+                if mmask[i] == 1
+                    # idxs[i] = k-length column indicies
+                    # weighted sum
+
+                    # what about mulitple missings??
+                    coli = div(i, size(dataT, 1)) + 1
+                    # println("$i $coli $(size(mdata))")
+                    w = sum(dists[coli]) ./ dists[coli]
+                    # Inverse distance weighting
+                    if isnan(sum(w)) || isinf(sum(w))
+                        # if some distance is zero, keep original value
+                        data[i] = data[i]
+                    else
+                        data[i] = sum(w .* dataT[idxs[coli]])
+                    end
+                end
+            end
+        end
+
+        return data
+    end
+end

test/runtests.jl

@@ -1,13 +1,15 @@
 using Impute
-using Tables
-using Test
 using AxisArrays
+using Combinatorics
 using DataFrames
 using Dates
+using Distances
+using Random
 using RDatasets
 using Statistics
 using StatsBase
-using Random
+using Tables
+using Test
 
 using Impute:
     Drop,
@@ -24,6 +26,15 @@ using Impute:
     interp,
     chain
 
+function add_missings(X, ratio=0.1)
+    result = Matrix{Union{Float64, Missing}}(X)
+
+    for i in 1:floor(Int, length(X) * ratio)
+        result[rand(1:length(X))] = missing
+    end
+
+    return result
+end
 
 @testset "Impute" begin
     # Defining our missing datasets
@@ -515,5 +526,35 @@ using Impute:
         end
     end
 
+    @testset "KNN" begin
+        # Test a case with few variable
+        # (e.g., only a few variables, only )
+        @testset "Data - few variables" begin
+            data = Matrix(dataset("Ecdat", "Electricity"))
+            X = add_missings(data)
+
+            knn_imputed = impute(copy(X), Impute.KNN(; num_nn=3, dist=Euclidean(), context=Context(; limit = 1.0)))
+            mean_imputed = impute(copy(X), Fill(; context=Context(; limit=1.0)))
+
+            # If we don't have enough variables then SVD imputation will probably perform
+            # about as well as mean imputation.
+            @test nrmsd(knn_imputed, data) > nrmsd(mean_imputed, data) * 0.9
+        end
+
+        @testset "Data - random variables" begin
+            M = rand(100, 200)
+            data = M * M'
+            X = add_missings(data)
+
+            knn_imputed = impute(copy(X), Impute.KNN(; num_nn=3, dist=Euclidean(), context=Context(; limit = 1.0)))
+            mean_imputed = impute(copy(X), Fill(; context=Context(; limit=1.0)))
+
+            # If most of the variance in the original data can't be explained by a small
+            # subset of the eigen values in the svd decomposition then our low rank approximations
+            # won't perform very well.
+            @test nrmsd(knn_imputed, data) > nrmsd(mean_imputed, data) * 0.9
+        end
+    end
+
     include("deprecated.jl")
 end