From d31962cf63b9bf5b42e6b28137adf0b37bb21c5e Mon Sep 17 00:00:00 2001
From: Milan Bouchet-Valat <nalimilan@club.fr>
Date: Mon, 8 Jun 2020 05:59:53 +0200
Subject: [PATCH] Fix minimum and maximum in the presence of missing values
 (#35989)

* Fix minimum and maximum in the presence of missing values

* Fix comment
---
 base/reduce.jl | 10 +++++-----
 test/reduce.jl | 12 ++++++++++++
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/base/reduce.jl b/base/reduce.jl
index 6d19fa50e3037..6582e72274aba 100644
--- a/base/reduce.jl
+++ b/base/reduce.jl
@@ -576,11 +576,11 @@ function mapreduce_impl(f, op::Union{typeof(max), typeof(min)},
     start = first + 1
     simdstop  = start + chunk_len - 4
     while simdstop <= last - 3
-        # short circuit in case of NaN
-        v1 == v1 || return v1
-        v2 == v2 || return v2
-        v3 == v3 || return v3
-        v4 == v4 || return v4
+        # short circuit in case of NaN or missing
+        (v1 == v1) === true || return v1
+        (v2 == v2) === true || return v2
+        (v3 == v3) === true || return v3
+        (v4 == v4) === true || return v4
         @inbounds for i in start:4:simdstop
             v1 = _fast(op, v1, f(A[i+0]))
             v2 = _fast(op, v2, f(A[i+1]))
diff --git a/test/reduce.jl b/test/reduce.jl
index 9501f41f8b77c..d640bcdde7440 100644
--- a/test/reduce.jl
+++ b/test/reduce.jl
@@ -341,6 +341,18 @@ A = circshift(reshape(1:24,2,3,4), (0,1,1))
 @test size(extrema(A,dims=(1,2,3))) == size(maximum(A,dims=(1,2,3)))
 @test extrema(x->div(x, 2), A, dims=(2,3)) == reshape([(0,11),(1,12)],2,1,1)
 
+@testset "maximum/minimum/extrema with missing values" begin
+    for x in (Vector{Union{Int,Missing}}(missing, 10),
+              Vector{Union{Int,Missing}}(missing, 257))
+        @test maximum(x) === minimum(x) === missing
+        @test extrema(x) === (missing, missing)
+        fill!(x, 1)
+        x[1] = missing
+        @test maximum(x) === minimum(x) === missing
+        @test extrema(x) === (missing, missing)
+    end
+end
+
 # any & all
 
 @test @inferred any([]) == false