From 27fe81db7016be451512c5a71517bb2f4a16ffce Mon Sep 17 00:00:00 2001
From: "Steven G. Johnson" <stevenj@mit.edu>
Date: Fri, 22 Aug 2014 13:01:20 -0400
Subject: [PATCH] add efficient mean and median for ranges

---
 NEWS.md        |  3 +++
 base/range.jl  | 17 +++++++++++++++++
 test/ranges.jl |  8 ++++++++
 3 files changed, 28 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 23b8921e78108e..b9011d537f071a 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -25,6 +25,8 @@ Library improvements
     intend to use the default `Forward` order, or
     `pq = PriorityQueue(KeyType, ValueType, OrderType)` otherwise.
 
+  * Efficient `mean` and `median` for ranges ([#8089]).
+
 Julia v0.3.0 Release Notes
 ==========================
 
@@ -947,3 +949,4 @@ Too numerous to mention.
 [#7654]: https://github.com/JuliaLang/julia/issues/7654
 [#7917]: https://github.com/JuliaLang/julia/issues/7917
 [#7992]: https://github.com/JuliaLang/julia/issues/7992
+[#8089]: https://github.com/JuliaLang/julia/issues/8089
diff --git a/base/range.jl b/base/range.jl
index 85ed100b3dded4..5193078b3631d0 100644
--- a/base/range.jl
+++ b/base/range.jl
@@ -553,6 +553,23 @@ function sum{T<:Real}(r::Range{T})
                                      : (step(r) * l) * ((l-1)>>1))
 end
 
+
+function mean{T<:Real}(r::Range{T})
+    isempty(r) && error("mean of an empty range is undefined")
+    (first(r) + last(r)) / 2
+end
+
+function median{T<:Real}(r::Range{T})
+    isempty(r) && error("median of an empty range is undefined")
+    n = length(r)
+    if iseven(n)
+        mid = n >> 1
+        return (r[mid] + r[mid+1]) / 2
+    else # odd
+        return float(r[(n+1)>>1])
+    end
+end
+
 function map!(f::Callable, dest, r::Range)
     i = 1
     for ri in r dest[i] = f(ri); i+=1; end
diff --git a/test/ranges.jl b/test/ranges.jl
index 3102b8dc4f9b7a..d860f229aff84b 100644
--- a/test/ranges.jl
+++ b/test/ranges.jl
@@ -350,3 +350,11 @@ end
 @test length(map(identity, 0x0001:0x0005)) == 5
 @test length(map(identity, uint64(1):uint64(5))) == 5
 @test length(map(identity, uint128(1):uint128(5))) == 5
+
+# mean/median
+for f in (mean, median)
+    for n = 2:5
+        @test f(2:n) == f([2:n])
+        @test_approx_eq f(2:0.1:n) f([2:0.1:n])
+    end
+end