added extrema(A,dims)

NEWS.md

@@ -111,6 +111,8 @@ Library improvements
 
     * Improve performance of `quantile` ([#14413]).
 
+    * `extrema` can now operate over a region ([#15550]).
+
   * The new `Base.StackTraces` module makes stack traces easier to use programmatically. ([#14469])
 
 Deprecated or removed

base/docs/helpdb/Base.jl

@@ -2082,13 +2082,6 @@ appended to an internal buffer of backtraces.
 """
 :@profile
 
-"""
-    extrema(itr)
-
-Compute both the minimum and maximum element in a single pass, and return them as a 2-tuple.
-"""
-extrema
-
 """
     isdigit(c::Union{Char,AbstractString}) -> Bool
 

base/reduce.jl

@@ -332,6 +332,11 @@ minabs(a) = mapreduce(AbsFun(), MinFun(), a)
 extrema(r::Range) = (minimum(r), maximum(r))
 extrema(x::Real) = (x, x)
 
+"""
+    extrema(itr) -> Tuple
+
+Compute both the minimum and maximum element in a single pass, and return them as a 2-tuple.
+"""
 function extrema(itr)
     s = start(itr)
     done(itr, s) && throw(ArgumentError("collection must be non-empty"))
@@ -353,6 +358,43 @@ function extrema(itr)
     return (vmin, vmax)
 end
 
+"""
+    extrema(A,dims) -> Array{Tuple}
+
+Compute the minimum and maximum elements of an array over the given dimensions.
+"""
+function extrema(A::AbstractArray, dims)
+    sz = [size(A)...]
+    sz[[dims...]] = 1
+    B = Array{Tuple{eltype(A),eltype(A)}}(sz...)
+    extrema!(B, A)
+end
+
+@generated function extrema!{T,N}(B, A::Array{T,N})
+    quote
+        sA = size(A)
+        sB = size(B)
+        @nloops $N i B begin
+            AI = @nref $N A i
+            (@nref $N B i) = (AI, AI)
+        end
+        Bmax = sB
+        Istart = ones(Int,ndims(A))
+        Istart[([sB...].==1) & ([sA...].!=1)] = 2
+        @inbounds @nloops $N i d->(Istart[d]:size(A,d)) begin
+            AI = @nref $N A i
+            @nexprs $N d->(j_d = min(Bmax[d], i_{d}))
+            BJ = @nref $N B j
+            if AI < BJ[1]
+              (@nref $N B j) = (AI, BJ[2])
+            elseif AI > BJ[2]
+              (@nref $N B j) = (BJ[1], AI)
+            end
+        end
+        B
+    end
+end
+
 ## all & any
 
 any(itr) = any(IdFun(), itr)

doc/stdlib/collections.rst

@@ -299,12 +299,18 @@ Iterable Collections
 
    Compute the minimum value of ``A`` over the singleton dimensions of ``r``\ , and write results to ``r``\ .
 
-.. function:: extrema(itr)
+.. function:: extrema(itr) -> Tuple
 
    .. Docstring generated from Julia source
 
    Compute both the minimum and maximum element in a single pass, and return them as a 2-tuple.
 
+.. function:: extrema(A,dims) -> Array{Tuple}
+
+   .. Docstring generated from Julia source
+
+   Compute the minimum and maximum elements of an array over the given dimensions.
+
 .. function:: indmax(itr) -> Integer
 
    .. Docstring generated from Julia source

test/reduce.jl

@@ -167,6 +167,10 @@ prod2(itr) = invoke(prod, Tuple{Any}, itr)
 @test maximum(collect(Int16(1):Int16(100))) === Int16(100)
 @test maximum(Int32[1,2]) === Int32(2)
 
+@test extrema(reshape(1:24,2,3,4),1) == reshape([(1,2),(3,4),(5,6),(7,8),(9,10),(11,12),(13,14),(15,16),(17,18),(19,20),(21,22),(23,24)],1,3,4)
+@test extrema(reshape(1:24,2,3,4),2) == reshape([(1,5),(2,6),(7,11),(8,12),(13,17),(14,18),(19,23),(20,24)],2,1,4)
+@test extrema(reshape(1:24,2,3,4),3) == reshape([(1,19),(2,20),(3,21),(4,22),(5,23),(6,24)],2,3,1)
+
 # any & all
 
 @test any(Bool[]) == false